Apple’s new watch sounds like a win for anyone interested in their heart health. It will notify wearers of a slow or irregular heart rhythm, and it can take a basic electrocardiogram (ECG), a recording of the electrical activity of the heart.

During Apple’s presentation of the new watch on Sept. 12, the company boasted of its FDA clearance and basked in praise from American Heart Association president Dr. Ivor Benjamin.

As a heart doctor, my opinion is that if you think an Apple Watch is nifty, buy one. But do not buy it for your health. It will not improve your health, and it could even bring you harm.

In particular, I’m concerned about the problems that arise when we screen healthy people.

“As a heart doctor, my opinion is that if you think an Apple Watch is nifty, buy one. But do not buy it for your health.”

I concede that early detection seems like a good idea, especially for atrial fibrillation (AF). AF can increase a person’s risk of stroke, and many people who have AF don’t know it. We also have effective ways to treat it, including drugs that block clotting—called anticoagulants—that can reduce the risk of stroke in patients with AF and other risk factors, such as high blood pressure or diabetes.

The first obstacle when it comes to AF screening is understanding that the vast majority of people do not have AF, but most people do have normal variation of their heart rhythm, which can mimic AF. Benign premature beats, for instance, can make your rhythm irregular.

This makes ECG accuracy a problem. Recently, I co-wrote an editorial in JAMA-Internal Medicine, where my co-authors and I reviewed studies of AF screening with medical-grade 12-lead ECGs, which are more accurate than the one-lead ECG used in the Apple Watch.

The specificity of an ECG (its ability to correctly identify people who don’t have AF) is around 90 percent. That may sound good, but the 10 percent of the time that an irregular rhythm is falsely labeled as AF will exert a massive effect in large populations—like the millions of people who may soon own the new Apple Watch.