There is a new version of Pulse Sensor code now up on the Pulse Sensor Code Downloads page! The new version (version 0.6) is a significant update and we advise everyone to use it. From our tests, it makes the Pulse Sensor more accurate and reliable on whole.
In detail, changes include:
A digital filter for better signal processing.
Automatic update of heart rate (BPM).
Automatic update of time between beats (HRV) with 1mS resolution !
Sensor data samples are taken every 1mS, timed by an interrupt generated by Timer1.
Access to both raw sensor data and filtered sensor data (b/c we know you want that) !
[Source] Hackedgadgets via http://pulsesensor.com/