MAX 30100 Heart-Rate Sensor Module

Working voltage: 1.8-5.5V
I2C INTERFACE
Complete Pulse Oximeter and Heart-Rate Sensor Solution Simplifies Design
Integrated LEDs, Photo Sensor, and High-Performance Analog Front –End
Ultra-Low-Power Operation Increases Battery Life for Wearable Devices
Programmable Sample Rate and LED Current for Power Savings
Ultra-Low Shutdown Current (0.7µA, typ)

The device has two LEDs, one emitting a red light, another emitting infrared light. For pulse rate, only the infrared light is needed.
Both the red light and infrared light is used to measure oxygen levels in the blood.

When the heart pumps blood, there is an increase in oxygenated blood as a result of having more blood.
As the heart relaxes, the volume of oxygenated blood also decreases. By knowing the time between the increase and decrease of oxygenated blood, the pulse rate is determined.
It turns out, oxygenated blood absorbs more infrared light and passes more red light while deoxygenated blood absorbs red light and passes more infrared light.
This is the main function of the MAX30100: it reads the absorption levels for both light sources and stored them in a buffer that can be read via I2C.

This board is ready for use with an Arduino. Just follow this wiring setup:
MAX30100    Arduino UNO
VIN        5V
GND       GND
SCL       A5
SDA       A4
INT       D2