Heart Rate Monitor

The circuit for sensing a heartbeat would be the same, no matter where the sensor is placed.

So, find a "heartbeat sensor" circuit that you can copy, and use that. _{You don't have a clue, do you?}

It might be better if you learned how to design the circuit yourself instead of asking strangers to do it for you.

I hope you are not going into the medical field.

You might have better luck finding an artery close to the back surface of the hand, rather than in the palm.

I have something for you to try. Go to a place where there is no background noise. Then, place your left palm over your left ear. Do you hear anything?

Next, place your right palm over your right ear. Do you hear anything?

Better think of another project.

Just stick an electrocardiogram sensor on each palm.

There are 3 possible techniques for registering the heart rate. The first is an ECG amplifier. You could use commercial ECG electrodes, but a brass or other metal bar is equally effective. The signal is of the order of a few millivolts, even when you put the reference electrode the other side of the heart, so you need a stable high-gain amplifier. If you are not running off a battery, then be very careful to isolate the input circuit from any possible fault voltage situations.
Moving away from the palm, the radial artery can be felt on the thumb side of the inside of the wrist. You could strap a pressure sensor over that and amplify that signal. the isolation requirement is not so severe.
Finally, you could shine a light through the tip of a finger towards a light sensor on the other side. The pulse cannot be felt in the finger, but the flow is still pulsatile, giving a varying density through which the light shines. This is part of the principle of pulse oximetry (which measures the blood oxygen saturation in addition to the pulse rate). Again, you will need to amplify a small signal, but the isolation requirement is not so severe.