Human heart pumps 70 cc of blood at each beat against a pressure of 125 mm of Hg. If the pulse frequency is 72 per minute, the power of the heart is nearly

p = pressure against which heart is pumping blood = p.g.h = 13.6 x ${10}^3$ x 10 x 125 x ${10}^{-3}$ N/$m^2$ ⇒17,000 N/$m^2$.
If A be the effective area of flow of blood, then resistive force F = p.A. If v be the average velocity of flow of blood, then power = Fv = pAv = p x (Av) = p x Q
= 17 x ${10}^3$ x 70 x ${10}^{-6}$W = 1.2W