|Now you can use your iPhone monitor your heart rate. This iPhone Heart Monitor app by John Ballinger. It uses the inbuilt microphone on your iPhone 3G or headphone microphone to listen to and detect your heart beats. You can use the iPhone 3G directly over your heart or directly on the pulse in your neck or wrist, the app will be able to detect the stats(Check out see the video). Available on iTunes for $5. [ link ]
Please Note: works best with iPhone 3G, works well with iPhone 1G/2G but you must use the headphone cable microphone, the inbuilt microphone does not detect heart beats.