hi
do you have the hardware yet for reading the heart rate? It can be very difficult to do. the only reliable way I have seen is with a Polar brand wireless monitor that was hacked to get the heart rate pulse. The other methods, ECG type and Pulse oximitry ( shining alight through a finger and reading the light that emergesz on the other side of the finger) don't work very well for pateints that move around. Pulse oximetry looks simple but in reality when you move your arm, there is a rush of blood that screws up the reading. I built a project like this once and after a few months of working on it concluded that yes, there is a reason that a medical grade heart-rate monitor costs thousands of dollars! 
D