Re: pulsing effect?

I think the best is to tie the Scale of the layer to a real heartbeat.

Import your heartbeat sound to your comp. Select it, then Animation>Keyframe Assistant>Convert Audio To Keyframes. This adds a new null named Audio Amplitude. Select it, hit "e" to reveal the Channel Sliders, twirl down the left, right or both channels.

Now in the layer to be pulsed, hit "s" to reveal the Scale Stopwatch, Alt Click that stopwatch, then drag the pickwhip (looks like an @) to the Audio Amplitudes Layer's Channel Slider (I like the both slider). You get an expression like this:

temp = thisComp.layer("Audio Amplitude").effect("Both Channels")("Slider");
[temp, temp]

Add "value +" to the beginning of the second line to get:

temp = thisComp.layer("Audio Amplitude").effect("Both Channels")("Slider");
value + [temp, temp]

This just lets the layer start at 100% scale and pulse up from there.

If the pulse isn't big enough, add "*2" to the end of the first line, that means "times 2", *4 means times 4, making ithe increase bigger by that much.

temp = thisComp.layer("Audio Amplitude").effect("Both Channels")("Slider")*2;
value + [temp, temp]

OR

You could just make one pulse with keyframes and add the loopOut expression:

loopOut("cycle", 0)

That will just keep repeating the 3 to 4 keyframes you used to set up one Scale Pulse.