Dozens of conditions can produce the pounding heartbeat, breathlessness, dizziness, and fatigue that people associate with atrial fibrillation. Some are other heart-rhythm disorders that look almost identical on a monitor. Others have nothing to do with the heart’s electrical system at all: an overactive thyroid, a panic attack, even a large hiatal hernia can create symptoms so similar that experienced clinicians sometimes need multiple tests to sort them out. Understanding the range of AFib look-alikes matters because each mimic has its own treatment, and mistaking one for another can mean taking the wrong medication or missing a condition that needs attention on its own terms.
Other Arrhythmias That Look and Feel Like AFib
The closest mimics are other irregular heart rhythms. AFib’s hallmark on an ECG is an “irregularly irregular” pattern with no organized atrial activity. A handful of other arrhythmias share some or all of those features, making them easy to confuse even for trained eyes.
Atrial flutter is probably the most common source of confusion. Flutter involves an organized electrical circuit in the atrium beating very rapidly, usually around 300 times per minute. The ventricles don’t keep up at that rate, so the heart’s conduction system blocks some of those impulses. When the blocking pattern is variable, the resulting heartbeat can look irregular enough to pass for AFib. Research using mathematical models of heart-rhythm patterns has shown that distinguishing flutter from AFib based on a short rhythm strip can be done with only moderate accuracy, roughly 84 to 89 percent sensitivity depending on heart rate, which means misidentification happens regularly in clinical settings.1Heart Rhythm. Discriminating atrial flutter from atrial fibrillation using a multilevel model of atrioventricular conduction Flutter and AFib also frequently coexist in the same person, which complicates things further.
Multifocal atrial tachycardia (MAT) is another rhythm that fools clinicians. Like AFib, MAT produces an irregularly irregular heartbeat with narrow-complex beats on an ECG. The two rhythms share enough visual features that MAT is widely considered a clinical imitator of AFib.2PubMed. How often is multifocal atrial tachycardia mistaken for atrial fibrillation in the emergency department? Depending on which ECG lead you’re looking at, the small P waves that technically distinguish MAT can be nearly invisible, making both disorders appear to lack organized atrial activity.3American Heart Journal. Multifocal atrial tachycardia: Mechanisms, clinical correlates, and treatment The distinction matters because MAT is strongly linked to lung disease and electrolyte problems, and its treatment focuses on fixing those underlying issues rather than the rhythm-control and blood-thinner strategies used for AFib.
Frequent premature atrial contractions (PACs) round out the arrhythmia mimics. Everyone has the occasional PAC, that “skipped beat” feeling. But when they occur very frequently, they create an irregular pulse pattern that can feel exactly like AFib. PACs that come in clusters are also recognized as a marker for later developing actual AFib, so they exist in a gray zone where the mimic may eventually become the real thing.4Cardiovascular Research. Frequent premature atrial contractions as a signalling marker of atrial cardiomyopathy, incident atrial fibrillation, and stroke
Thyroid Problems and Hormonal Storms
An overactive thyroid is one of the most important non-rhythm conditions to rule out when AFib is suspected. Excess thyroid hormone speeds up the heart, causes palpitations and breathlessness, and genuinely does increase the risk of AFib itself. But it also commonly produces sinus tachycardia, a fast but regular rhythm that still feels like a pounding, racing heart. Someone with undiagnosed hyperthyroidism may show up with textbook AFib symptoms: fatigue, exercise intolerance, a fluttering sensation in the chest, shortness of breath. A review of multiple studies confirmed that AFib and sinus tachycardia are the most common rhythm problems linked to excess thyroid hormones.5PubMed Central. Hyperthyroidism and the Risk of Cardiac Arrhythmias: A Narrative Review This dual nature means hyperthyroidism can both mimic AFib (through fast sinus rhythm and symptoms) and actually cause it.
A rarer but more dramatic hormonal mimic is pheochromocytoma, a tumor of the adrenal gland that dumps adrenaline-like chemicals into the bloodstream in surges. These episodes produce sudden spikes in heart rate and blood pressure, palpitations, sweating, headaches, and a sense of dread. The cardiovascular effects come from overstimulation of the receptors that control heart rate and blood vessel tone.6Cardiology in Review. Cardiovascular Manifestations of Pheochromocytoma While the most well-known cardiac sign is high blood pressure, these tumors can also trigger actual arrhythmias and produce abnormal rhythms that cause palpitations and neck pounding similar to AFib episodes.7PubMed Central. A unique cardiovascular presentation of pheochromocytoma Pheochromocytomas are rare, but when a younger patient presents with episodic palpitations, sweating, and high blood pressure, they should be on the list.
Electrolyte Imbalances
Low magnesium deserves its own mention because it sits at a crossroads: it can both cause arrhythmias directly and make other rhythms harder to control. Magnesium plays a central role in stabilizing the electrical activity of heart cells. When levels drop, the heart becomes electrically unstable, leading to extra beats, rapid rhythms, and irregular patterns that can feel identical to AFib. Correcting magnesium levels is also one of the standard approaches to controlling the ventricular rate during actual AFib, which speaks to how intertwined the two issues are.8PubMed Central. The Role of Hypomagnesemia in Cardiac Arrhythmias: A Clinical Perspective Low potassium and other electrolyte shifts produce similar instability. These are among the most fixable causes of AFib-like symptoms, which is why a basic blood panel is one of the first things ordered when palpitations bring someone to the emergency room.
Heart Failure With Preserved Pumping Strength
Heart failure doesn’t always mean a weak pump. In the type known as HFpEF (heart failure with preserved ejection fraction), the heart squeezes normally but doesn’t relax and fill properly. The resulting symptoms, breathlessness with exertion, fatigue, swollen ankles, and exercise intolerance, overlap almost perfectly with AFib. Both conditions become more common with age, frequently occur together, and share risk factors like high blood pressure and obesity. When a patient has both, teasing apart which symptoms belong to which condition becomes genuinely difficult.9PubMed. Heart Failure With Preserved Ejection Fraction and Atrial Fibrillation: Vicious Twins
The practical problem here is that both conditions are common in the same population (older adults with high blood pressure), and each one makes the other worse. AFib can raise the pressures inside the heart and worsen HFpEF symptoms, while HFpEF stretches the atria in ways that promote AFib. Someone who has been told they have AFib but whose symptoms don’t improve with rate control may actually have undiagnosed HFpEF driving most of their breathlessness and fatigue.
Lung Disease and the Overlap With AFib
Chronic obstructive pulmonary disease (COPD) creates a symptom picture that overlaps with AFib in ways that can stump even specialists. The core symptoms of moderate-to-severe COPD, shortness of breath, fatigue, and reduced exercise tolerance, are indistinguishable from what many AFib patients experience. Making matters harder, the two conditions frequently coexist: COPD increases the risk of developing AFib, and AFib is common in people with severe lung disease. As one interdisciplinary review put it, telling the two apart can be particularly challenging in older patients who smoke and complain of nonspecific symptoms like breathlessness and fatigue.10European Heart Journal. Chronic obstructive pulmonary disease and atrial fibrillation: an interdisciplinary perspective
COPD also produces its own rhythm disturbances. The hypoxia, elevated pressure in the lung’s blood vessels, and medications used to treat COPD (particularly certain bronchodilators) can trigger MAT and other atrial arrhythmias. So a person with COPD may have palpitations that are from a lung-related rhythm disturbance rather than AFib, or they may have genuine AFib triggered by their lung disease, or they may simply have COPD symptoms being misread as cardiac. Each scenario calls for a different approach.
Obstructive Sleep Apnea
Sleep apnea is one of the most underappreciated sources of AFib-like symptoms. When the airway collapses during sleep, the resulting drops in oxygen trigger surges of adrenaline-like activity and create strong negative pressure inside the chest. Both mechanisms directly disturb the heart’s rhythm. People with obstructive sleep apnea experience a higher burden of various rhythm disturbances, including premature beats, pauses in the heartbeat, and episodes of true AFib.11PubMed Central. Cardiac rhythm disorders in obstructive sleep apnea
The symptom overlap goes beyond the rhythm itself. Untreated sleep apnea leaves people fatigued, lightheaded, short of breath on exertion, and foggy-headed, which are all symptoms that patients and doctors might attribute to AFib. Even the nighttime awakenings that some AFib patients report (waking with a racing heart) can look identical to what happens during an apnea event. Treating sleep apnea often improves or eliminates rhythm disturbances that were blamed on a primary cardiac problem.
Panic Attacks and Anxiety Disorders
The symptom list for a panic attack reads like a near-perfect copy of an AFib episode: a racing or pounding heartbeat, chest tightness, dizziness, tingling in the hands, shortness of breath, and a feeling that something is seriously wrong.12PubMed Central. Panic attacks and supraventricular tachycardias: the chicken or the egg? Panic attacks affect roughly 2 percent of the general population, and the cardiovascular symptoms during an attack can be intense enough to send someone to the emergency room convinced they’re having a heart problem.
The relationship between panic and arrhythmias is more tangled than simple mimicry, though. Adrenaline released during a panic attack can genuinely trigger short runs of rapid heart rhythm, which in turn intensifies the panic, creating a feedback loop. Some people who are eventually diagnosed with a real arrhythmia, including AFib, spent years being told their symptoms were “just anxiety.” And some people who undergo extensive cardiac workups for palpitations turn out to have a panic disorder and a completely normal heart. The challenge for both patients and clinicians is that neither diagnosis rules out the other.
Gastrointestinal Triggers
This one surprises most people. A large hiatal hernia, where part of the stomach slides upward through the diaphragm and sits near the heart, can mechanically irritate the heart and provoke palpitations. In one well-documented case, a patient had worsening palpitations specifically after eating. She was found to have a high burden of premature ventricular contractions linked to her hiatal hernia and gastroesophageal reflux. After extensive cardiac investigation ruled out a primary heart problem, surgical repair of the hernia resolved the rhythm disturbance entirely.13PubMed Central. Rare and unusual presentation of gastrocardiac syndrome
Gastrocardiac syndrome, as this phenomenon is sometimes called, likely works through a combination of mechanical pressure on the heart from the displaced stomach and vagal nerve reflexes triggered by distention and acid exposure. It’s not common, but it’s worth thinking about when palpitations reliably follow meals, especially large ones or meals eaten lying down. Bloating and acid reflux as accompanying symptoms are a useful clue.
Medications and Substances That Trigger Rhythm Disturbances
A wide range of medications can provoke arrhythmias, and not just the ones most clinicians would immediately suspect. A scientific statement from the American Heart Association noted that drugs can trigger AFib, atrial flutter, atrial tachycardia, and several other rhythm disturbances, and that many clinicians are less familiar with this drug-arrhythmia link than they should be.14Circulation. Drug-Induced Arrhythmias: A Scientific Statement From the American Heart Association
Common culprits include stimulants (both prescription and recreational), certain asthma and COPD medications, some antibiotics, and a surprisingly long list of heart medications that can paradoxically cause the very rhythm problems they’re meant to treat. Alcohol is another well-known trigger: “holiday heart” is the colloquial term for AFib episodes brought on by heavy drinking, but even moderate alcohol in sensitive individuals can provoke palpitations and irregular rhythms. Caffeine, despite its reputation, has a more nuanced relationship with AFib than most people think; moderate intake doesn’t appear to increase risk for most people, but in those already prone to arrhythmia, it can tip the balance.
The practical point is that when AFib-like symptoms appear for the first time, a careful medication review and substance-use history is essential. Stopping or adjusting the offending substance sometimes resolves the problem entirely.
Pericarditis and Cardiac Inflammation
Inflammation of the sac surrounding the heart, known as pericarditis, is typically recognized by sharp chest pain that changes with position and breathing. But it also causes palpitations, and it can trigger genuine AFib. In a study of over 800 consecutive cases of acute pericarditis, about 4 percent developed atrial fibrillation or flutter, usually within the first 24 hours of symptoms. In roughly three-quarters of those cases, the arrhythmia resolved on its own.15PubMed. Incidence and prognostic significance of new onset atrial fibrillation/flutter in acute pericarditis
Myocarditis, inflammation of the heart muscle itself (often from a viral infection), can produce a similar picture: palpitations, chest discomfort, fatigue, and rhythm disturbances including AFib-like rapid rhythms. The key distinction is that pericarditis- and myocarditis-triggered arrhythmias tend to resolve once the inflammation settles, unlike AFib driven by structural changes in the atria, which tends to recur.
Postural Tachycardia Syndrome
POTS is a condition where standing up causes an abnormally large jump in heart rate, often by 30 beats per minute or more. The resulting symptoms, pounding heartbeat, lightheadedness, breathlessness, fatigue, and brain fog, overlap heavily with AFib. Many POTS patients end up on heart monitors to look for arrhythmias. In one review of over 300 ambulatory rhythm monitors worn by POTS patients, arrhythmias were detected on about 15 percent of recordings.16Cardiology in the Young. Cardiac arrhythmias in postural tachycardia syndrome and orthostatic intolerance That means most POTS patients’ symptoms are from the autonomic dysfunction itself rather than a true arrhythmia, but it also means a meaningful minority do have rhythm problems layered on top of POTS, which complicates diagnosis.
POTS tends to affect younger people, especially women, whereas AFib is overwhelmingly a condition of middle-aged and older adults. A 25-year-old woman with palpitations, dizziness, and fatigue is far more likely to have POTS or a related autonomic condition than AFib, but the symptom profile alone can’t tell you which one it is.
When the Monitor Itself Is the Problem
In the age of consumer health technology, a new category of AFib mimic has emerged: the false positive. Smartwatches and fitness trackers detect AFib by analyzing the pulse pattern at your wrist using light-based sensors. These sensors work well under ideal conditions, but movement, a loose watch band, sweating, and certain skin conditions can corrupt the signal. When that happens, the software may interpret motion-related noise as an irregular rhythm and flag it as possible AFib.17PubMed Central. Electrocardiographic artifact potentially misleading to the wrong management
Even in clinical settings, ECG artifacts from muscle tremor, poor electrode contact, or patient movement can mimic arrhythmia patterns on a monitor. One study of false AFib alerts from smartwatches found that among 35 false alerts investigated, more than half were caused by noisy signals during normal sinus rhythm, and about a third were triggered by benign rhythm variations like premature beats and sinus arrhythmia rather than AFib.18PubMed Central. False Atrial Fibrillation Alerts from Smartwatches are Associated with Decreased Perceived Physical Well-being and Confidence in Chronic Symptoms Management That same study found that receiving false alerts was associated with decreased physical well-being and reduced confidence in managing chronic symptoms, a real consequence of a technology artifact.
Developers are working on better algorithms to filter out motion noise before making a determination, including using the watch’s built-in accelerometer to detect when the wrist is moving too much for a reliable reading.19PubMed Central. Atrial Fibrillation Detection from Wrist Photoplethysmography Signals Using Smartwatches In the meantime, if your smartwatch flags AFib, the right response is to follow up with your doctor for a medical-grade ECG rather than to start worrying immediately. A single alert from a wrist device is a prompt for further testing, not a diagnosis.
Why Getting the Right Diagnosis Matters Practically
AFib’s specific risks and treatments make accurate diagnosis unusually consequential. True AFib substantially increases the risk of stroke, and most AFib patients are considered for blood thinners to prevent clots from forming in the fibrillating atria. If the actual problem is panic attacks, POTS, or artifact on a smartwatch, taking a blood thinner exposes you to bleeding risk for no benefit. Conversely, if a real arrhythmia is being written off as anxiety, you’re missing a condition with real stroke implications.
The path to clarity usually involves wearing a heart monitor for an extended period (anywhere from 24 hours to a couple of weeks) to catch the rhythm during an episode. Blood tests for thyroid function, electrolytes, and kidney function help rule out metabolic triggers. If sleep apnea is suspected, an overnight sleep study can identify it. And if a smartwatch was the starting point, a clinical-grade ECG during symptoms is the necessary confirmation step. Many of the conditions discussed here are eminently treatable once correctly identified, from fixing low magnesium to repairing a hiatal hernia to adjusting medications. The first step is making sure the label fits.