A PAC, or premature atrial contraction, is an extra heartbeat that fires earlier than expected from the upper chambers of your heart. It’s one of the most common types of irregular heartbeat, and in most cases it’s completely harmless. Nearly everyone experiences PACs at some point, though many people never notice them. If you felt a skipped beat, a flutter, or a strange thump in your chest and started searching, a PAC is likely what you’re reading about.
How a PAC Happens
Your heart has a built-in pacemaker, a cluster of cells in the upper right chamber that sends a steady electrical signal telling the heart when to beat. With a PAC, a different spot in one of the upper chambers (the atria) fires off a signal before the pacemaker gets its turn. This creates an early, slightly out-of-rhythm beat.
Because the beat comes too soon, the heart hasn’t had time to fill completely with blood. The result is a weaker-than-normal contraction followed by a brief pause while the heart resets. That pause is often more noticeable than the early beat itself, which is why many people describe the sensation as a “skipped” beat rather than an extra one. The next beat after the pause tends to feel stronger than usual because the heart had a moment longer to fill.
What PACs Feel Like
Some people feel nothing at all. Others describe a flip-flopping sensation in the chest, a sudden flutter, or the feeling that the heart “stopped for a second” before thumping hard. You might notice it more when you’re lying down at night or sitting quietly, simply because there are fewer distractions. During exercise or busy moments, the same PACs can go completely unnoticed.
The sensation can be alarming, especially the first time it happens. But the feeling itself, even if it repeats several times a day, doesn’t necessarily mean anything is wrong with your heart.
Common Triggers
PACs have a long list of known triggers, and most of them are things you can identify in your own daily routine:
- Caffeine and stimulants: Coffee, energy drinks, and some pre-workout supplements are classic triggers.
- Alcohol: Even moderate drinking can increase the frequency of extra beats.
- Stress and anxiety: Elevated stress hormones make the heart more electrically irritable.
- Poor sleep or fatigue: Sleep deprivation alone can bring on episodes.
- Dehydration: Not drinking enough water shifts your electrolyte balance, which affects the heart’s electrical system.
- Low potassium or magnesium: These minerals are essential for normal heart rhythm. When levels drop, extra beats become more likely.
- Tobacco and recreational drugs: Both are well-established triggers.
- Certain medications: Some drugs used for heart conditions or mental health can provoke PACs as a side effect.
People who are sedentary, chronically stressed, or regularly short on sleep tend to have more frequent PACs. In many cases, addressing one or two of these triggers is enough to reduce episodes significantly.
How PACs Are Detected
A standard electrocardiogram (EKG) can catch a PAC if one happens during the few seconds you’re hooked up to the machine. On the readout, a PAC shows up as an early beat with an abnormally shaped electrical wave, different from the pattern your heart’s natural pacemaker produces. Sometimes the early beat’s signal hides inside the previous heartbeat’s wave, creating a subtle “camel hump” shape that trained eyes look for.
Because PACs often come and go unpredictably, a single EKG may miss them entirely. In that case, doctors use portable monitors you wear for 24 to 48 hours (or longer) that continuously record your heart’s rhythm. These monitors are especially useful for matching the timing of your symptoms to what your heart is actually doing at that moment. Some newer wearable devices and smartwatches can also flag irregular rhythms, though they’re less precise than medical-grade monitors.
When PACs Matter
For the vast majority of people, PACs are a nuisance at most. Occasional extra beats, those making up less than 1% of your total heartbeats, are considered minimal and rarely need any attention beyond reassurance.
Frequency starts to matter when PACs become more persistent. Researchers categorize PAC burden by the percentage of total heartbeats that are premature: less than 1% is minimal, 1% to under 5% is occasional, and 5% or higher is considered frequent. At higher burdens, there’s an association with an increased risk of developing atrial fibrillation, a more sustained irregular rhythm that can carry its own health consequences. High-burden PACs have also been linked in research to subtle effects on cognitive function over time, likely because of their connection to atrial fibrillation risk.
This doesn’t mean that everyone with frequent PACs will develop problems. It means that if monitoring shows a consistently high burden, your doctor may want to keep a closer eye on your heart rhythm over the years.
Red Flags Worth Knowing
Most PACs don’t require emergency care, but certain symptoms alongside palpitations deserve prompt attention. Sudden loss of consciousness, significant dizziness or lightheadedness during a racing heart, and chest pain are all reasons to seek immediate evaluation. A family history of sudden cardiac death at a young age or known inherited heart conditions also raises the stakes, even if symptoms seem mild. In these situations, PAC-like sensations could be masking a different, more serious rhythm problem that looks similar from the outside.
Managing PACs
Treatment depends entirely on how frequent and bothersome the PACs are. For most people, the best approach is identifying and reducing triggers. Cutting back on caffeine, improving sleep habits, managing stress, staying hydrated, and avoiding alcohol are often enough to bring noticeable relief. Regular physical activity also helps stabilize heart rhythm over time.
If lifestyle changes aren’t enough and PACs are significantly affecting quality of life or happening at a high frequency, doctors may prescribe medications that calm the heart’s electrical activity, typically drugs that slow the heart rate slightly and make it less reactive to stray signals. These are generally well tolerated and effective at reducing the sensation of extra beats, even if they don’t eliminate every PAC entirely.
In rare cases where PAC burden is very high and medications don’t help, a procedure called catheter ablation can target and disable the specific spot in the atrium that’s firing the extra signals. This is uncommon for PACs alone and is usually reserved for situations where the extra beats are triggering more serious rhythm problems or weakening the heart over time.