It's a real heartbeat (not a drum machine)

It’s a real human heartbeat, recorded by engineer Alan Parsons and then processed to give it that thump.

The story goes that Parsons recorded a friend’s heartbeat on a reel-to-reel tape machine. No fancy synths, no samples from a library – just a microphone and a chest. He then ran it through a low-pass filter to take out the high frequencies, leaving that deep, almost exaggerated thud you hear at the start and end of “The Dark Side of the Moon.”

There’s a persistent myth that it’s Paul McCartney’s heartbeat, but that’s not true. McCartney