ezFitHm is an application for the iPhone that monitors your heart rate. It works with an ezFitHm receiver (dongle) and with any 5.3Khz heart rate monitor chest straps.
It is designed to work for many hours and save all your heart rate data into a zoomable graph. And you can enjoy your music in iPhone during exercise.
ezFitHm does not claim to be, nor intends to be, a medical or clinical application.