Heartrate Circuit

I wanted to receive clarification on the behavior of the LED in the circuit found at the following link provided by ADI: (wiki.analog.com/.../alm-lab-heart-rate-mon). Should the LED be flashing regardless of my finger placement, and should it be picking up ambient light? Or should it only flash when placing my finger above the IR LED and Phototransistor? I see it flashing differently if I place my finger, but want to see how I can reduce the effects of flashing when not placing my finger.