A PAC, or premature atrial contraction, is an extra heartbeat that starts in the upper chambers of your heart slightly earlier than it should. It feels like a skipped beat, a flutter, or a brief thump in your chest. PACs are extremely common and, in most cases, completely harmless.
How a PAC Happens
Your heart has a built-in pacemaker called the sinus node, located in the upper right chamber. It sends out electrical signals in a steady rhythm that tells your heart when to beat. A PAC occurs when a different spot in the upper chambers fires off a signal before the sinus node gets its turn. This creates an early, slightly out-of-sync contraction that briefly interrupts your normal rhythm before the sinus node takes back over.
These rogue signals frequently originate from the pulmonary veins, the blood vessels that carry blood from your lungs back to your heart. The early beat itself is often weaker than a normal beat because the heart hasn’t had time to fill with as much blood. After the PAC, there’s typically a short pause before the next normal beat. That pause, and the stronger-than-usual beat that follows it, is what most people actually feel.
What PACs Feel Like
Many people with PACs never notice them at all. When you do feel them, the most common sensation is a “skipped beat” or a flip-flopping feeling in your chest. Some people describe it as a sudden thud followed by a brief pause, or a fluttering sensation near the throat or chest. The feeling can be startling, but it usually lasts only a second or two.
PACs can also cause a vague sense of unease, lightheadedness, or awareness of your heartbeat that you don’t normally have. If they happen repeatedly over minutes or hours, some people feel mildly short of breath or fatigued, though this is less common with occasional PACs.
How Common Are PACs?
Nearly everyone has PACs at some point. When researchers monitor hearts over a 24-hour period, PACs show up in close to 100% of older adults and about 73% of younger people. Most of these go completely unnoticed. A typical person without heart complaints might have around 100 PACs per day without ever feeling a thing.
They become more frequent with age and are slightly more common in people with high blood pressure, heart disease, or lung conditions. But having PACs does not mean you have an underlying heart problem.
Common Triggers
Several everyday factors can increase the frequency of PACs:
- Caffeine and alcohol: Both can make the upper chambers of the heart more electrically irritable.
- Stress and poor sleep: High adrenaline states make ectopic signals more likely to fire.
- Dehydration and electrolyte shifts: Low magnesium and potassium levels have been linked to more frequent premature beats.
- Stimulant medications: Decongestants, certain asthma inhalers, and some supplements can provoke extra beats.
For many people, reducing or eliminating these triggers noticeably reduces how often PACs occur.
When PACs Matter
Isolated PACs in a structurally normal heart are considered benign. They don’t damage the heart or shorten your life. The picture changes, though, when PACs become very frequent. Researchers define “frequent” PACs as more than 720 in a 24-hour period. In studies, people in the frequent category averaged over 2,500 PACs per day, compared to around 100 per day in the infrequent group.
A high PAC burden has been linked to an increased risk of developing atrial fibrillation, a sustained irregular rhythm in the upper chambers that does carry health consequences. This doesn’t mean frequent PACs will inevitably lead to atrial fibrillation, but it’s one reason doctors pay closer attention when the daily count is high. People with frequent PACs and other risk factors like high blood pressure or an enlarged left atrium are typically monitored more closely.
How PACs Are Detected
A standard electrocardiogram (EKG) can catch a PAC if one happens during the brief recording. On the tracing, the extra beat shows up as a heartbeat that arrives too early, with a slightly different-looking electrical wave at the start compared to your normal beats. If your PACs are intermittent, a doctor may order a Holter monitor, a portable device you wear for 24 to 48 hours that records every heartbeat and counts exactly how many PACs you’re having.
The location of the rogue signal affects the electrical pattern. If the early beat originates near the bottom of the upper chamber, close to the electrical relay station between upper and lower chambers, the interval between the initial wave and the main heartbeat is shorter than normal. If it comes from higher up or farther away, that interval stretches longer. These details help doctors pinpoint where the extra beats are coming from.
Managing Frequent PACs
When PACs are infrequent and not causing significant symptoms, no treatment is needed. The first step for bothersome PACs is almost always lifestyle modification: cutting back on caffeine and alcohol, improving sleep, managing stress, and staying well hydrated.
Magnesium supplementation is sometimes recommended, though the evidence is mixed. One pilot trial found no reduction in PAC counts after 12 weeks of daily magnesium compared to placebo. However, a separate two-phase study found that while magnesium didn’t cure the arrhythmia, it was associated with fewer premature beats and improved symptoms. The results suggest magnesium may help some people, particularly those whose levels are low to begin with, but it’s not a reliable fix for everyone.
For people with very frequent, highly symptomatic PACs that don’t respond to lifestyle changes, doctors may prescribe medications that slow electrical conduction and reduce irritability in the heart’s upper chambers. In rare cases where PACs are extremely frequent and originate from a single identifiable spot, a catheter-based procedure can target and disable that focus. But the vast majority of people with PACs never need anything beyond reassurance and trigger management.