LV is a pressure-generating pump which endures pressure overload, while RV is a flow-generating pump intolerant of pressure overload. Therefore, RV pump function (but not RV myocardial contractility) can easily fail in face of severe pulmonary arterial hypertension (PH) because of increased afterload. Available indexes of RV function are load dependent and incapable of accurately reflecting RV myocardial contractility. Animal RV in which myocardium is damaged extensively by either soldering iron or coronary occlusion can work well without causing systemic congestion or decreased SV. In clinical settings, evaluation of pre-treatment RV function in patients with PH has limited value in predicting prognosis. Furthermore, in virtually all patients with PH after successful lung transplantation, RV function has been reported to improve indicating that deteriorated RV function in patients with PH is due to an increase in RV afterload, but not to decreased RV myocardial contractility. In view of these facts, evaluation of RV function seems hardly useful in patients with PH.