There are two terms to remember. Myocardial oxygen demand and myocardial oxygen supply. Hb concentration is a factor for oxygen supply. 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 proportional Contractility- Directly proportional Intramyocardial tension- Directly proportional After load- Directly proportional Preload- Directly proportional Wall thickness- Inversely proportional