How do you pair a heart rate monitor/chest strap with the Apple Watch series 3

Hi there, mrsguz.

I see that you're wanting to track your heart rate using your Polar chest strap. It connects using Bluetooth, so you'd like to pair it with your Apple Watch Series 3. I'm happy to help.

Set up your Apple Watch -- Your Apple Watch works in tandem with your iPhone.

To use Apple Watch Series 3 (GPS + Cellular), you need an iPhone 6 or later with the latest version of iOS. (To use Apple Watch Series 3 (GPS) or earlier models of Apple Watch, you need an iPhone 5s or later with the latest version of iOS.)

Your heart rate. What it means, and where on Apple Watch you’ll find it. -- Your Apple Watch will measure your heart rate and you can view your resting, walking, breathe, workout and recovery rates.

Polar Beat on the App Store -- If you're using a Polar H10 or Polar OH1 Heart Rate Sensor, there's an iPhone and Apple Watch app available to track your fitness.

Get started - iPhone User Guide -- You can also track your heart rate using the Health application on your iPhone.

Collect data from Apple Watch. After you pair Apple Watch with your iPhone, data is automatically sent to Health. To view your move, exercise, and stand data and goals, tap Health Data, then tap Activity. To view heart rate data, tap Health Data, then tap Heart.

Collect data from another device. Follow the setup instructions for the device. If it’s a Bluetooth device, you need to pair it with iPhone. See Connect Bluetooth devices.

Use the Health app on your iPhone or iPod touch -- Review the information in this article on how to use the Health application on your iPhone.

Take care, and enjoy your day!