With the Heart Rate app, you can check your heart rate anytime you want. Open the app and wait for Apple Watch to measure your heart rate. You can also check your heart rate at rest, while walking, while breathing, exercising and recovering throughout the day. To easily open the app, add the Heart Rate complication to the watch face or add the Heart Rate app to the Dock.
You can also turn on heart rate notifications, so you know if your heart rate exceeds or drops below a set threshold (in beats per minute, BPM), or to occasionally check for irregular heart rhythms.
Irregular heart rhythm notifications are only available with watchOS 5.1.2 or later. Enabling Irregular Heart Rhythm Notifications is only possible if the feature is available in your country or region and if you are in the country or region where you purchased the device.
Find out where irregular heart rhythm notifications are available.When Apple Watch measures your heart rateHeart measurements in the Health app on iPhone and resting heart rate on Apple Watch
When you use the Workout app, Apple Watch continuously measures your heart rate during exercise and for the next 3 minutes to determine your heart rate during recovery. If you don’t see your heart rate, check your settings.
This information, along with other data collected, allows Apple Watch to estimate the number of calories burned. Additionally, Apple Watch measures your heart rate throughout the day when you are resting and periodically when you are walking (Apple Watch Series 1 or later).
Since Apple Watch takes these readings in the background based on what you’re doing, the timing between measurements will vary. The Apple Watch also calculates a daily resting and walking average rate, combining background heart rate reading with accelerometer data as soon as enough background readings are available. You can control which third-party apps have access to your health data in the Health in Sources app.
The displayed data may include anomalies that may occasionally cause measurement values to be too high or too low.The Apple Watch’s optical heart rate sensor uses a technology called photoplethysmography.
Although the name is difficult, the principle behind it is very simple: blood is red because it reflects red light and absorbs green light. Apple Watch uses green LED lights paired with light-sensitive photodiodes to detect the amount of blood flowing into your wrist at any given time. With each beat of the heart, the blood flow in the vessels of the wrist increases and, as a result, more green light is absorbed.
Between one beat and the next, the flow is less, as is the absorption of green light. By blinking the LED lights hundreds of times per second, Apple Watch can calculate how many times the heart beats each minute, thus measuring the heart rate. The optical heart rate sensor supports a range of 30 to 210 beats per minute. In addition, it is designed to compensate for low signal levels by increasing the brightness of the LEDs and the sampling rate.