A) heat
B) chemical
C) electrical
D) heat, chemical, electrical, mechanical
Correct Answer: D
Solution :
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 consumption by the heart is an excellent measure of the chemical energy liberated while the heart performs its work. During heart muscle contraction, most of the expended chemical energy is converted into heat and a much smaller portion into work output. The ratio of work output to total chemical energy expenditure is called the efficiency of cardiac contraction, or simply efficiency of the heart. Maximum efficiency 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.
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