A racing heart has dozens of possible causes, ranging from a cup of coffee to a serious heart rhythm disorder. In adults, a heart rate above 100 beats per minute at rest is considered tachycardia. Understanding why your heart speeds up starts with knowing what’s normal: for most adults, a resting heart rate falls between 60 and 100 bpm, though well-trained athletes can sit comfortably in the 40s or 50s.
How Your Nervous System Controls Heart Rate
Your heart rate is largely governed by a tug-of-war between two branches of your nervous system. The sympathetic branch speeds things up, and the parasympathetic branch slows things down. When the sympathetic side fires, nerve endings in the heart release norepinephrine, a chemical messenger that latches onto receptors on heart muscle cells. This triggers a cascade of changes: calcium floods into cells faster, the heart contracts more forcefully, and the pace quickens.
At the same time, sympathetic activation suppresses the calming signals from the parasympathetic side. A peptide released by sympathetic nerves actually blocks the release of acetylcholine, the chemical responsible for slowing the heart. So when your body decides it needs a faster heart rate, it hits the gas and cuts the brakes simultaneously. This system works perfectly when you’re exercising or facing a genuine threat, but it can misfire in response to stress, illness, or substances that mimic those chemical signals.
Stress, Anxiety, and Panic Attacks
Emotional stress is one of the most common reasons people notice their heart racing. Anxiety activates the same sympathetic nervous system response as physical danger, flooding your bloodstream with adrenaline and norepinephrine. Your heart doesn’t distinguish between a bear chasing you and a looming work deadline.
During a full panic attack, the effect can be dramatic. Heart rates can spike to 200 beats per minute or higher. One key difference between a panic-driven racing heart and one caused by a heart attack: heart attacks tend to follow physical exertion, like shoveling snow or climbing stairs, while panic attacks are tied to emotional triggers. That said, the symptoms can feel nearly identical in the moment, which is part of what makes panic attacks so frightening.
Caffeine, Alcohol, and Nicotine
Caffeine is the substance people most commonly blame for a racing heart, but the relationship is more nuanced than you’d expect. In typical amounts (a few cups of coffee per day), caffeine does not appear to significantly increase the risk of heart rhythm disturbances, even in people prone to atrial fibrillation. Energy drinks with very high doses of caffeine are a different story and are worth avoiding if you’re sensitive to heart rate changes.
Alcohol is a more reliable trigger. For people with a history of irregular heart rhythms, keeping intake to no more than three drinks per week is a common recommendation. Nicotine stimulates the release of norepinephrine directly, which raises heart rate through the same pathway your nervous system uses during a stress response. Even nicotine replacement products like patches and gum can produce this effect, though usually to a lesser degree than smoking.
Medications That Speed Up the Heart
Several common medications increase heart rate as a side effect. Asthma inhalers are a prime example. Short-acting rescue inhalers work by activating the same type of receptors that adrenaline targets. While these receptors are concentrated in the lungs (where they open airways), they also exist in the heart. After using a rescue inhaler, your heart rate can rise steeply and take over two hours to return to your normal range. Long-acting inhalers can have a similar, more sustained effect.
Other medications known to speed up the heart include stimulants used for ADHD, certain antidepressants, decongestants containing pseudoephedrine, and some thyroid medications if the dose is too high. If you notice a new pattern of racing heart after starting or changing a medication, that connection is worth exploring with your prescriber.
Thyroid Problems
An overactive thyroid (hyperthyroidism) is one of the most important medical causes of a persistently racing heart. Thyroid hormone has a direct effect on heart muscle cells, altering the behavior of sodium, potassium, and calcium channels that control heart rhythm. It also lowers resistance in blood vessels throughout the body, which triggers a compensatory increase in heart rate and blood volume.
The effect is substantial. In hyperthyroidism, the heart’s output can increase 50% to 300% above normal. A fast resting heart rate is the most common rhythm disturbance in the condition and appears in nearly all patients with an overactive thyroid. If your heart races consistently, even when you’re calm and rested, thyroid function is one of the first things worth checking.
Dehydration and Anemia
When your blood volume drops, whether from dehydration, blood loss, or anemia, your heart compensates by beating faster to maintain adequate blood flow to your organs. Dehydration reduces the total volume of fluid in your bloodstream, so each heartbeat delivers less blood. The only way to keep up is to increase the number of beats per minute.
Anemia works through a similar mechanism. With fewer red blood cells carrying oxygen, the heart has to pump faster to deliver enough oxygen to tissues. Iron deficiency anemia is particularly common in women of reproductive age and often goes unrecognized for months. A racing heart during mild activity, like climbing a flight of stairs, can be an early clue.
Heart Rhythm Disorders
Sometimes a racing heart isn’t just the heart beating faster in response to a trigger. It’s an electrical malfunction within the heart itself. Two of the most common culprits are atrial fibrillation and supraventricular tachycardia (SVT).
Atrial Fibrillation
In atrial fibrillation, chaotic electrical signals fire more than 300 times per minute in the heart’s upper chambers, causing them to quiver instead of contracting in an organized way. The lower chambers beat irregularly in response. It primarily affects people 65 and older, and up to 90% of episodes may cause no noticeable symptoms at all, which means many people have it without knowing.
Supraventricular Tachycardia
SVT is different. It produces a very fast but regular rhythm, with rates as high as 200 beats per minute. The problem originates from an abnormal electrical signal above the heart’s lower chambers, often in the node that connects the upper and lower chambers. SVT can strike at any age, including in young children, though the average age of diagnosis is 45. Brief episodes feel like a flip-flopping or fluttering sensation in the chest. Longer episodes can cause dizziness, shortness of breath, or fainting.
How a Racing Heart Gets Evaluated
The challenge with diagnosing a racing heart is that it often isn’t happening when you’re sitting in a doctor’s office. The first step is usually an electrocardiogram (ECG), a quick, painless test where sticky patches on your chest record the heart’s electrical activity. If the ECG looks normal (which it often does, because the episode has passed), the next step is typically a portable monitor.
A Holter monitor is a small device you wear for one to two days while going about your normal routine. It records every heartbeat, catching irregularities that a single ECG might miss. If your episodes happen less than once a week, an event recorder may be a better option. You wear it for a longer period and activate it when you feel symptoms. In some cases, an echocardiogram (an ultrasound of the heart) is ordered to check for structural problems that could be driving the rhythm disturbance.
Warning Signs That Need Immediate Attention
Most episodes of a racing heart are harmless and resolve on their own. But certain combinations of symptoms signal something more serious. Call emergency services if your heart won’t stop racing and you experience any of the following: passing out, chest pain or pressure that spreads to your neck, jaw, or arms, or difficulty breathing. Other concerning signs include dizziness, confusion, unusual sweating, or episodes that are becoming more frequent or more intense over time. These don’t always mean something dangerous is happening, but they warrant prompt evaluation.