The Green Easy Pulse Sensor Heart Beat Sensor HRM2511E is a DIY pulse sensor that is designed for hobbyists and educational applications, It is used to illustrate the principle of phot plethysmography (PPG), PPG is a non-invasive technique for detecting the cardio-vascular pulse wave from a fingertip. The Easy Pulse Sensor uses a transmission mode PPG probe (HRM-2511E) sensor.

This Sensor uses an infrared light source to illuminate the finger on one side, and On the other side of the sensor there is a photodetector that measures small variations in the transmitted light intensity due to changes in blood volume inside the tissue.
 
The onboard components & instrumentation provide a clean and filtered analog PPG waveform.
The on-board LED also indicates the digital pulse output.
The analog and digital signals are both synchronous with the heartbeat.
Features of Easy Pulse Sensor:
Stable PPG signal output (Generate Phot plethysmography PPG with Arduino)
MCP6004 Op amp based instrumentation with rail-to-rail output capability for maximum output signal swing
Separate analog & digital outputs
Potentiometer gain control for the analog output
Pulse width control for the digital output
Additional test points on board for analyzing signals at different stages of instrumentation
Output as +3.3V & +5V
Simple to interface Easy Pulse Sensor with Arduino & any other Microcontroller.