The chief resident-in-training at our hospital was
putting a patient on a bypass mechine in preparation
for open-heart surgery.

The patient, who happened to be a policeman, had his
aorta clamped, and then circulation was stopped so
that the operation could be done on a nonbeating heart.

The atmosphere in the operating room had been serious
until the clamp was applied.  Just then the attending
physician remarked, "Hey---you just arrested a cop!"