Chemical Energy Required for Cardiac Contraction: Oxygen Utilization by the Heart
Heart muscle, like skeletal muscle, uses chemical energy to provide the work of contraction. This energy is derived mainly from oxidative metabolism of fatty acids and, to a lesser extent, of other nutrients, especially lactate and glucose. Therefore, the rate of oxygen con-sumption by the heart is an excellent measure of the chemical energy liberated while the heart performs its work.
Efficiency of Cardiac Contraction. During heart muscle con-traction, most of the expended chemical energy is con-verted into heat and a much smaller portion into workoutput. The ratio of work output to total chemicalenergy expenditure is called the efficiency of cardiaccontraction, or simply efficiency of the heart. Maximumefficiency of the normal heart is between 20 and 25 per cent. In heart failure, this can decrease to as low as 5 to 10 per cent.