"Heart doc vs engine mechanic" joke

A mechanic was removing a cylinder head from the motor
of a Harley motorcycle when he spotted a well-known
heart surgeon in his shop. The surgeon was there
waiting for the service manager to come take a look at
his bike.
The mechanic shouted across the garage, "Hey Doc, can
I ask you a question?"
The surgeon, a bit surprised, walked over to the
mechanic working on the motorcycle.
The mechanic straightened up, wiped his hands on a rag
and asked, "So Doc, look at this engine. I open its
heart, take valves out, fix' em, put' em back in, and
when I finish, it works just like new. So how come I
get such a small salary and you get the really big
bucks, when you and I are doing basically the same
work?
The surgeon paused, smiled and leaned over, and
whispered to the mechanic..... "Try doing it with the
engine running".