Can I use IR Transmitter/Receiver for heart beat detecting?
No, you cannot.  The sensor you link to has a circuit which attempts to detect IR light modulated at a specific frequency, and produces a digital output.   For a heartbeat sensor you need an analog output to feed into far more sophisticated signal processing - effectively the built-in processing gets in the way and means you cannot use it for this purpose.

Additionally, sensors of this type typically have an automatic gain control which means that they desensitize when subjected to continuous signal - they are designed for sources like remote controls where the modulation is itself pulsed on an off in small fractions of a second, so they interpret constant modulated light as noise and soon turn off their output.