<prompt> All of the following statements about myocardial oxygen demand is true, exceptCorrelates with heart rateIs proportional to external cardiac workIs negligible when heart is at restDepends upon duration of systole  <response>: Oxygen demand depends on the work being done. The work done is to pump the blood which is in the ventricles preload against the resistance in the aorta afterload. So, myocardial oxygen demand depends onRate Directly proportionalContractility Directly proportionalIntramyocardial tension Directly proportionalAfter load Directly proportionalPreload Directly proportionalWall thickness Inversely proportionalThe oxygen demand of myocardium is not having the same change with varying external works. But it is proportional to the external work. 