The PM5 performance monitor can display your heart rate during training if used with compatible equipment. It is not necessary to use a separate heart rate watch monitor if you just want to view your heart rate on the PM5. You simply pair your heart rate belt with the monitor.
Bluetooth Smart, ANT+ and Suunto ANT will work and transmit data to the PM5 monitor. Beware that Bluetooth Smart is another technology than ordinary Bluetooth.
The Polar H7 Bluetooth Smart Chest Belt ( paid link ) is compatible with the PM5 and a good option if you plan to monitor your heart rate with a compatible smart phone app too during other activities.
Knowing your heart rate and training zones will allow you to work to a training program that specifies what heart rate you should aim for, ensuring you achieve optimal improvement.