What Is ECG on a Smartwatch? How It Works and What to Check

What an ECG measures

An electrocardiogram (ECG or EKG) records the timing and strength of the electrical signals that make the heart beat. In a clinical setting, electrodes are placed on your arms, legs, and chest, and the resulting waveform shows the P wave, QRS complex, and T wave, which correspond to the upper chambers contracting, the lower chambers contracting, and the heart recovering. This information helps a doctor see how fast your heart beats, whether the rhythm is steady, and the strength of the signals passing through each part of the heart (MedlinePlus).

A smartwatch ECG is a simplified version. Instead of the 12-lead setup used in hospitals, it uses a single lead created by electrodes in the watch and your finger. This captures a one-dimensional view of the heart's electrical activity, which is enough to identify certain rhythm irregularities but not to diagnose all conditions. The result is a recording you can share with your doctor for interpretation.

How a smartwatch records an ECG

To take a recording with the Apple Watch, you open the ECG app, rest your arms on a table or in your lap, and hold a finger on the Digital Crown for 30 seconds. The back sensor and the crown act as two electrodes, capturing the electrical pulses from your heart as they travel through your body. The app then checks whether the upper and lower chambers of your heart are beating in rhythm (Apple).

The recording is saved as a PDF that you can share with your doctor. You can take it at any time, especially when you feel symptoms like a rapid or skipped heartbeat. The process is painless and does not require any special setup beyond making sure the watch is snug on your wrist and your hands are clean and dry (Apple).

What the results mean

After a successful 30-second recording, the Apple Watch ECG app returns one of several classifications. A sinus rhythm result means your heart is beating in a uniform pattern between 50 and 100 beats per minute, with the upper and lower chambers in sync. This result applies only to that specific recording and does not guarantee a consistent pattern all the time, nor does it mean you are healthy (Apple).

An atrial fibrillation (AFib) result indicates an irregular heartbeat, which is a common form of serious arrhythmia. The app can detect AFib between 50 and 120 BPM in version 1 of the app and between 50 and 150 BPM in version 2. If you receive an AFib classification and have not been diagnosed with AFib, you should talk to your doctor (Apple).

The app may also return a low or high heart rate result, which affects its ability to check for AFib, or an inconclusive result if the recording cannot be classified. An inconclusive result can occur if you have a pacemaker or implantable cardioverter defibrillator, if other arrhythmias are present, or if the signal is too weak. In version 2, a Poor Recording classification means the recording quality was insufficient; repositioning your arm and ensuring the watch is snug and dry can help (Apple).

Limitations and what to verify before relying on it

Smartwatch ECGs are not diagnostic tools. The results reflect only what happens during the 30-second recording and cannot detect all heart conditions, such as heart attacks or structural problems. According to MedlinePlus, an EKG result alone cannot diagnose a heart condition; a doctor needs to combine it with other tests and your medical history.

The Apple ECG app is not intended for use by people under 22 years old, and it may be inconclusive if you have a pacemaker or implantable cardioverter defibrillator (Apple). Also, the app is not available in all countries or regions, so you should verify that the feature is supported where you live.

Before relying on a smartwatch ECG for health decisions, check whether the feature has regulatory clearance. The FDA distinguishes between general wellness products that support a healthy lifestyle and medical devices that are intended to diagnose, treat, or prevent disease. ECG features designed to detect atrial fibrillation may fall under the latter category, and manufacturers may seek FDA clearance or approval. Review the manufacturer's documentation to understand what the ECG feature is intended for and whether it claims to diagnose any condition (FDA).

Choosing a smartwatch with ECG

If you want to monitor your heart rhythm between doctor visits, look for a watch with an ECG feature that fits your lifestyle and ecosystem. Consider battery life, display quality, and how easily you can share recordings with your healthcare provider. For Apple users, our best Apple smartwatches guide highlights models with the ECG app. If you use an Android phone, explore best Wear OS smartwatches or best Samsung smartwatches for options with ECG capability.

When evaluating any smartwatch with ECG, confirm that the feature is cleared or authorized by a relevant regulatory body if you plan to use it for medical insights. You can also check the manufacturer's specifications to see if the ECG app is available in your country and whether it requires a specific watch model or software version. For a broader look at certified health devices, see our best certified brands smartwatches guide.

What to pick for your use

Questions

Is a smartwatch ECG as accurate as a hospital ECG?

No. A smartwatch ECG uses a single lead and captures only 30 seconds of activity, while a hospital ECG uses 12 leads and a longer recording. It can detect clear rhythm irregularities like AFib, but it cannot diagnose all heart conditions. Always interpret results with a doctor.

Can a smartwatch ECG detect a heart attack?

No. Smartwatch ECG apps are designed to identify atrial fibrillation and record rhythm, not to detect heart attacks. According to MedlinePlus, a clinical ECG can help diagnose conditions like heart attacks, but the interpretation requires a healthcare provider and additional tests.

Can I use a smartwatch ECG if I have a pacemaker?

It may give an inconclusive result. Apple states that having a pacemaker or implantable cardioverter defibrillator can cause the recording to be unclassifiable. If you have such a device, consult your doctor before relying on a smartwatch ECG.

Do I need a prescription to use a smartwatch ECG?

No. Smartwatch ECG apps are available directly on the device and do not require a prescription. However, they may be regulated as medical devices in some regions, and you should check whether the feature has the appropriate regulatory clearance for medical use.

What should I do if I get an AFib result?

If you receive an AFib classification and have not been diagnosed with AFib, you should talk to your doctor. The app's result is not a diagnosis but an indication that your heart rhythm may be irregular during the recording.