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How accurate is your heart rate monitor?

Wrist-worn heart rate monitors like the Apple Watch and the Fitbit Charge have become extremely popular among fitness buffs and cardiac patients.

But the devices might not be entirely accurate, according to a new study.

Researchers at the Cleveland Clinic had 50 people wear EKG chest strap and wrist heart monitors while walking on a treadmill.

Although the wrist monitors were accurate during rest periods, that precision decreased with more exercise.

None of the wrist devices were as accurate as the chest strap monitors.

Experts say wrist monitors are OK for recreational use, but heart patients should not rely on their readings.