This video shows how to create an infrared heart sensor using an Arduino controller, a couple of resistors, and an infrared light emitter and detector. This device will be used on the subject's finger, detecting the amount of blood which is flowing through the subject's finger. The amount of oxygenation of the blood is shown in the finger, which will cause the infrared light to reflect off the skin and to the transmitter which is close by. The fluctuations of oxygenation are picked up by the sensor, which you should wire to the Arduino. By observing the fluctuations in these signals, you are able to detect the heart rate of the subject.