The work done by the heart is 1 joule per beat.calculate the power of the heart if it beats 72 times in 1 min?

Treat as a units conversion problem. "times" represents beats, and one minute is 60 sec. We use sec because the usual unit of power is watt (Whaattt?) A watt is joule/sec. So start with 1 joule / beat, cancel out beats and convert min to sec Wha La !