I have achieved this heartbeat with a cheap contact mic (£20 on E.bay!) borrowed from a friend and placed it in between 2 soft cloths. Laid it, then, on an empty cardboard box and gently tapped the box.
Once recorded in Pro Tools I have applied a low pass filter and cut 24dB/oct @ 120Hz + a high pass filter with a cut of 24dB/oct at 29Hz. Boost of 3dB at 65Hz. Passed it though a reverb and a phaser and reversed the waves.
Thanks for “feeling it”!