PAC on Apple Watch ECG — what it means and what to do

If ECG+ identified a PAC in your recording, take a breath — premature atrial contractions are one of the most common heartbeat variations found in healthy people. Most people who have them don't even feel them.

A PAC is simply a heartbeat that fires a little early from the upper chambers of the heart. Your heart resets itself naturally after each one, and normal rhythm resumes straight away.

What does a PAC feel like?

Many people never feel them. When they are noticeable, a PAC typically feels like:

• A brief flutter or a skipped beat
• A slightly stronger beat immediately after the pause — the heart catching up
• An occasional brief awareness of your heartbeat

These sensations pass quickly and on their own are not a sign that something is wrong.

How ECG+ identifies a PAC

On your Apple Watch ECG, a PAC shows up as a beat that arrives earlier than the surrounding rhythm, often with a slightly different shape. ECG+ marks each one with an badge — the A stands for atrial — so you can see exactly where the premature beats occurred in your recording.

Here is another example — the early beat stands out clearly from the regular rhythm on either side:

PAC patterns you might see

Sometimes PACs appear on their own, and sometimes they fall into a repeating pattern. ECG+ names these so you have the right words if you speak with a doctor:

ECG+ also calculates your PAC burden — the share of all beats that are PACs — so you can track how things change across recordings over time.

PAC vs PVC — what is the difference?

Your ECG+ report may show both PACs and PVCs, and it is worth understanding what sets them apart. Both are early beats, but they come from different parts of the heart.

A PAC originates in the atria — the upper chambers — so the beat follows the heart's normal electrical pathway and looks relatively ordinary on the ECG. A PVC originates in the ventricles — the lower chambers — and travels a different electrical route, producing a wider, more prominent wave.

In practice, PVCs often feel more noticeable — that heavy thump is more pronounced because the compensatory pause is slightly longer. PACs tend to be subtler. That said, neither is inherently more serious than the other for most people. ECG+ tracks them separately so you can see which type appears in your recordings and how often.

Things that can bring on PACs

PACs often have a direct cause, and identifying yours can be genuinely useful. Common triggers include:

• Caffeine — coffee, energy drinks, strong tea
• Poor sleep or fatigue
• Stress or anxiety
• Alcohol
• Dehydration
• Intense exercise, especially if you are not well rested

If you notice PACs appearing after any of these, that pattern is worth noting and mentioning to your doctor.

Should I be concerned?

For most people, occasional PACs need no treatment. It is always worth mentioning them to your doctor, particularly if they are happening often, if the pattern has changed, or if they come with dizziness or chest discomfort. Your doctor can advise whether anything further is needed — and in most cases, the answer is simply to monitor and keep an eye on things.

What ECG+ gives you is real data to bring to that conversation, rather than just a description of how you felt.

A good next step

1. Take a few more recordings over the coming days to see whether PACs appear consistently or only occasionally.
2. Note any triggers — what you ate, drank, or were doing before recordings where PACs appear.
3. Share with your doctor — ECG+ lets you export your recordings as a PDF report, which gives your doctor something concrete to look at.

Frequently asked questions