Traditionally the right ventricle has been thought to function poorly in the presence of an increased afterload. Indeed, the presence of pulmonary arterial hypertension, or cor pulmonale, has been associated with a poor prognosis in patients with hypoxic chronic obstructive pulmonary disease (COPD). Recent data suggest that right ventricular contractility as measured by the right ventricular end-systolic pressure/volume relationship is relatively normal in patients with COPD, despite the presence of pulmonary arterial hypertension if the patients are studied when clinically stable, but reduced when the patients present with oedema. Continuous oxygen therapy is the only treatment which has been shown to improve survival in patients with COPD and cor pulmonale. However, the effects of oxygen therapy may not be directly related to an improvement in cardiac function.