Cardiograph is a universal app that purports to measure your heart rate via the cameras built into the iPhone or iPad 2. The app has a very slick-looking user interface reminiscent of a real-world electrocardiogram, complete with authentic (and irritating) sound effects, including the always-unnerving sound of a flatline.
The app functions similarly to a pulse oximeter, measuring blood flow through a finger placed over the camera and converting that into a pulse rate. Cardiograph has support for multiple profiles
