arduino heart beat rate measurement and display working on a project of taking heart beat rate and display on a 16*2 lcd display.which is a widely used sensor and its codes?how to get the threshold values?plz any one to help

Here is a example using a polar bluetooth hrm.

If you google "arduino heart rate monitor" you will find a lot of useful stuff. For the sensors there are - Bluetooth sensors - 433 MHz wireless sensors - Simple sensors using leds and photodiodes and detecting he change of translucense in you fingertip or earsnib