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.
Correlates with heart rate
Is proportional to external cardiac work
Is negligible when heart is at rest
Depends upon duration of systole