This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Nervous system, Subject name: Physiology
Which of the following statements about myocardial oxygen demand is true? 
Select and explain. 
A. Correlates with hea rate, B. Is directly propoional to external cardiac work, C. Is negligible when hea is at rest, D. Depends upon duration of systole
A: Correlates with hea rate
Answer: A: Correlates with hea rate 
Explanation: Myocardial oxygen demand is the amount of oxygen that the hea requires to maintain optimal function, and myocardial oxygen supply is the amount of oxygen provided to the hea by the blood which is controlled by the coronary aeries Ref: guyton and hall textbook of medical physiology 12 edition page number:246,247,248