All of the following statements about myocardial oxygen demand is true, except

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 on Rate – Directly proportional Contractility – Directly proportional Intramyocardial tension – Directly proportional After load – Directly proportional Preload – Directly proportional Wall thickness – Inversely proportional The oxygen demand of myocardium is not having the same change with varying external works. But it is proportional to the external work.