keyestudio XD-58C pulse sensor module is used to measure heart rates. It’s widely applied for students, artists, athletes, inventors, games or mobile terminal developers to develop heart rate related interactive works. 

You can wear the sensor on your finger or earlobe and connect it to Aduino. It also has an open source APP program that can display your heart rate real-time in graph. It’s in short, a heart rate sensor integrated with optical amplifier and noise elimination circuit.