Answer
1 watt.
Work Step by Step
The work done during 1 heartbeat is the force on the fluid, multiplied by the distance that the fluid moves. This is also equal to pressure times volume.
$$Power=\frac{PV}{t}$$
$$=\frac{(105mm-Hg)(\frac{133\;N/m^2}{1\;mm-Hg})(70\times10^{-6}m^3)}{(\frac{1}{70}min)(\frac{60\;s}{min})}\approx\;1W$$
