This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Cardiovascular system, Subject name: Physiology
Myocardial oxygen demand depend upon 
Select and explain. 
A. Preload, B. Afterload, C. Intramyocardial tension, D. Myocardial muscle mass
B: Afterload
Answer: B: Afterload 
Explanation: Oxygen consumption has also been shown to be nearly propoional to the tension that occurs in the hea muscle during contractionOxygen consumption has also been shown to be nearly propoional to the tension that occurs in the hea muscle during contraction multiplied by the duration of time that the contraction persists, called the tension-time indexRef: Guyton and Hall Textbook of Medical Physiology (12th Edn) page No:209