Premature atrial contractions (PACs) happen when a spot in the upper chambers of your heart fires an electrical signal before the heart’s natural pacemaker does, briefly interrupting your normal rhythm. They’re extremely common, and most people experience them at some point. The causes range from everyday triggers like caffeine and stress to underlying heart conditions, and understanding what’s behind them can help you figure out whether yours are harmless or worth investigating.
How PACs Happen in Your Heart
Your heartbeat is controlled by a small cluster of cells in the upper right chamber called the sinus node. This node acts as a natural pacemaker, sending out electrical impulses in a steady, organized rhythm. Each impulse travels through the upper chambers (the atria), telling them to contract and push blood into the lower chambers.
A PAC occurs when a different group of cells somewhere else in the atria fires off an impulse ahead of schedule. This premature signal causes the upper chambers to contract too early, often followed by a brief pause before the next normal beat. That pause is what most people feel as a “skipped beat” or a flutter in the chest. In people without structural heart problems, these rogue signals frequently originate from the pulmonary veins, the blood vessels that carry oxygenated blood from the lungs back to the heart.
Everyday Triggers
For many people, PACs are set off by substances or habits rather than a heart problem. The most well-known triggers include caffeine, nicotine, and alcohol. These stimulants can make atrial cells more electrically excitable, increasing the chance that a rogue impulse fires before the sinus node does. You don’t need to consume large amounts for this to happen. Even moderate intake in sensitive individuals can increase PAC frequency.
Sleep deprivation and dehydration also play a role. When your body is under-rested or low on fluids, your electrolyte balance shifts and your nervous system becomes more reactive, both of which can make the atria more prone to misfiring. Exercise, while generally heart-healthy, can temporarily increase PACs during or immediately after intense activity due to surges in adrenaline.
Stress and the Nervous System
Your heart doesn’t operate in isolation from your brain. The sympathetic nervous system, which controls your fight-or-flight response, directly influences how your heart’s electrical system behaves. Research from Cedars-Sinai has shown that people with irregular heart rhythms have elevated sympathetic nerve activity when experiencing symptoms like palpitations, dizziness, and chest discomfort. Importantly, this heightened nerve activity can trigger symptoms even when the heart is in a normal rhythm, meaning your nervous system alone can provoke the sensation of skipped beats.
Chronic stress, anxiety, and panic disorders keep the sympathetic nervous system in a state of heightened activity for extended periods. This persistent stimulation makes the atrial tissue more irritable and more likely to produce premature beats. It’s one reason why PACs often cluster during stressful periods and improve when stress is managed.
Medications That Can Cause PACs
Several classes of medication are known to increase PAC frequency. According to Yale Medicine, the list includes:
- Beta-agonists used to treat COPD and asthma
- Digoxin, a heart failure medication
- Some chemotherapy drugs
- Tricyclic antidepressants and MAO inhibitors
- Certain over-the-counter cold medications, particularly those containing decongestants
- Some weight-loss drugs
- Beta-blockers used for high blood pressure (paradoxically, despite being used to treat some arrhythmias)
Many of these drugs work by stimulating the same pathways that adrenaline uses, which directly increases atrial excitability. If you’ve noticed new or worsening palpitations after starting a medication, the timing is worth paying attention to.
Structural Heart Conditions
PACs are frequently seen in people with structural heart disease. Conditions that stretch, scar, or enlarge the atrial walls change the electrical properties of the tissue, making it easier for abnormal impulses to form and spread. High blood pressure is a major contributor because it forces the heart to work harder over time, gradually remodeling the left atrium. Valve disease, cardiomyopathy (weakened heart muscle), and prior heart surgery can all have the same effect.
A large population study published in Circulation found that people with existing cardiovascular disease had roughly 2.4 times the rate of PACs compared to those without. The study also found that elevated levels of certain proteins released when heart muscle is under stress were strongly linked to PAC frequency, reinforcing that subclinical heart damage, even when you don’t feel it, can drive these extra beats. Obesity and hypertension were identified as the two most important modifiable risk factors, largely because of the structural changes they cause to the left atrium over time.
Sleep Apnea and Breathing Disorders
Obstructive sleep apnea has a strong and well-documented connection to PACs. During an apnea episode, your airway closes temporarily, causing oxygen levels to drop. This triggers a cascade of responses: your sympathetic nervous system surges, your blood pressure spikes, and the walls of your atria experience sudden changes in pressure. Over time, these repeated episodes cause the atrial tissue to remodel physically, making it more susceptible to abnormal electrical signals.
Research published in the American Heart Association’s journal Circulation: Arrhythmia and Electrophysiology found that sleep apnea is associated with increased PACs and that treating sleep apnea may improve or even reverse arrhythmias by modifying the underlying factors that provoke them. If you experience frequent PACs and also snore heavily, wake up tired, or have daytime sleepiness, untreated sleep apnea could be a contributing factor.
When PAC Frequency Matters
Nearly everyone has occasional PACs, and in most cases they’re completely benign. But frequency matters. A study in the Journal of the American Heart Association found that having more than 76 PACs per day was an independent predictor of developing atrial fibrillation, a more sustained and clinically significant irregular rhythm. People above that threshold had about 1.75 times the risk of new-onset atrial fibrillation compared to those with fewer PACs.
This doesn’t mean that 76 beats per day is a danger line for every individual. It’s a statistical threshold that proved useful for predicting outcomes in a large study population. What it does suggest is that a consistently high PAC burden isn’t something to dismiss, especially if you have other risk factors like high blood pressure, obesity, or a family history of heart rhythm problems. Frequent PACs can sometimes be the first visible sign of atrial remodeling that hasn’t yet progressed to a more serious arrhythmia.
Idiopathic PACs: No Clear Cause
In many people, PACs occur without any identifiable structural disease or obvious chemical trigger. These are classified as idiopathic, and they tend to originate from the pulmonary veins. The exact reason some people’s pulmonary vein tissue becomes electrically active while others’ doesn’t is not fully understood, but it likely involves subtle differences in the electrical properties of the cells at the junction where the pulmonary veins meet the left atrium. This area is naturally prone to electrical instability, which is why it’s also the most common target for catheter ablation procedures that treat atrial fibrillation.
If your PACs have been evaluated and no underlying cause was found, the extra beats themselves are generally not dangerous. They can still be uncomfortable and anxiety-provoking, but their presence alone, when structural problems have been ruled out, is reassuring rather than alarming.