Amplifier in cardiac pulse meter
I think you are confused about the rate of the heart beat and the frequency content of your signal. You are filtering at a frequency that is too low to pass the heart beat signal. Try filtering with a low-pass cutoff of 10Hz or 20Hz instead.

Generally, these kinds of devices (photoplethysmographs) use an infrared LED and an infrared phototransistor. A phototransistor will give a much faster response than an LDR.

BTW, you aren't really observing a change in the flux of the blood, I think the capillaries expand a bit with each heartbeat so the volume of blood through which the light passes will increase.