Dr. Bob's joke

A motorcycle mechanic was removing a cylinder head from the motor of a Harley when he spotted a well-known cardiologist in his shop. The cardiologist was there waiting for the service manager to come and take a look at his bike when the mechanic shouted across the garage, "Hey Doc, take a look at this" The cardiologist, a bit surprised walked over to where the mechanic was working on the motorcycle. The mechanic straightened up, wiped his hands on a rag and said, "So Doc, look at this engine. I opened its heart, took the valves out, repaired or replaced anything damaged, and then put everything back in, and when I finished, it worked just like new. So how is that I make $30,000 a year and you make a million when you and I are doing basically the same work?"
The cardiologist paused, leaned over, and then whispered to the mechanic, "Try doing it with the engine running."