What is atrial fibrillation?

Atrial fibrillation (AFib) is the most common cardiac arrhythmia. It occurs when the upper chambers of the heart (the atria) beat irregularly instead of in a steady rhythm. AFib is one of the leading causes of stroke, heart failure, and cardiovascular complications worldwide.

AFib can come and go (paroxysmal) or be persistent. Many people with AFib have no symptoms, which is why early detection matters — it allows your doctor to assess your risk and discuss preventive measures.

How are signs of AFib detected?

Your watch uses a PPG (photoplethysmography) sensor that emits green light and measures its reflections on the blood vessels in your wrist. Changes in blood flow create a pulse signal that reveals your heart rhythm pattern.

Every 10 minutes, an algorithm analyzes your pulse signal. If an irregular rhythm suggestive of atrial fibrillation is detected, you receive a notification on your watch and in the Withings App. This feature is designed to supplement — not replace — a clinician's decision to screen for possible AFib.

What should you do?

• Record an ECG — When you receive a notification, your watch will suggest taking an ECG recording. The ECG measures the electrical activity of your heart directly and can confirm or rule out AFib with high accuracy.
• Understand the results — AFib is known to be intermittent, so a single ECG may not always confirm the alert. If the ECG shows a different result, it does not mean the original notification was wrong — AFib episodes can come and go.
• Contact your doctor — Share your notification and ECG recordings with your healthcare professional. You can export a PDF from the Withings App. If you have not been diagnosed with AFib before, this is especially important.

When to seek urgent care

If you experience chest pain, pressure, tightness, sudden shortness of breath, fainting, or what you think may be a heart attack, call emergency services immediately. This feature cannot detect heart attacks or other acute cardiac events.

Important to know

• Not a diagnosis — This assessment identifies episodes of irregular heart rhythm suggestive of atrial fibrillation. It is not a diagnosis and is intended to supplement a clinician's decision to screen for possible AFib.
• Not continuous monitoring — The feature checks periodically, not constantly. It cannot detect all instances of AFib, and people with AFib may not always receive a notification.
• Pacemaker or implanted device — Do not use this feature if you have a cardiac pacemaker, implantable defibrillator, or other implanted electronic device.
• Other arrhythmias — This feature is not recommended for users with other known arrhythmias, as it is specifically designed to look for signs of atrial fibrillation.