Myocardial oxygen demand depend upon:

A, B, C i.e. Preload, Afterload, Intramyocardial tension, Myocardial muscle mass > Blood Hb concentration Anemia, anxiety, aerio-venous fistula (AVF), beriberi, hypehyroidism, paget's disease, pregnancy, and pulmonary disease commonly cause high cardiac output due to reduced total peripheral resistane. Anemia decreases total peripheral resistance by reducing viscosity of blood (d/t decreased RBC concentation) and causing local vasodilation (d/t diminished delivery of O2 to tissue). Long term increased work load (but not so much excess that damages the hea) causes the hea muscle to increase in mass and contractile strength in the same way that heavy exercise causes skeletal muscle to hyperophy.