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The heart health feature on Apple Watch that many people may not know exists

Apple Watch has a Cardio Fitness feature that estimates your VO2 Max level to reflect long-term heart health, and can alert you if your level falls below the threshold—but many users never knew it was there

Many people use their Apple Watch to track their heart rate regularly, but did you know the watch has another hidden feature that measures heart health on a deeper level? It's called Cardio Fitness—a measure of the fitness of your heart and blood vessels.

This feature works by estimating your VO2 Max (the maximum amount of oxygen your body can use during exercise), an indicator of long-term cardiovascular health that doctors and athletes have relied on for years. The higher the value, the better your body delivers oxygen to your muscles—reflecting a strong, healthy heart.

Unlike other features, it doesn't require you to manually start a measurement. Apple Watch uses its heart rate sensor together with GPS and the accelerometer to automatically estimate the value while you're walking outdoors, running, or hiking—without needing to push yourself to your limit.

What's particularly interesting is the alert system. If a user's Cardio Fitness level falls below the standard threshold for their age and sex, the watch can send an early notification, which may serve as a signal to start taking care of your heart health sooner rather than later.

Users can view their Cardio Fitness history and enable notifications through the Health app on iPhone. Apple also has official support documentation clearly explaining how to set it up. If you already own an Apple Watch but have never tapped in to check, take a look and see where your heart fitness level stands.