What's the difference between a cylinder-head and your heart?

Question by Reba GG: What's the difference between a cylinder-head and your heart?
A mechanic was removing a cylinder-head from the
motor of a Harley motorcycle when he spotted a well-known
cardiologist in his shop.

The cardiologist was there waiting for the service manager
to come take a look at his bike when the mechanic shouted
across the garage, "Hey Doc, want to take a look at this?"

The cardiologist, a bit surprised, walked over to where the
mechanic was working on the

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