Most commonly, right- side heart failure is cause by left-side heart failure, as any increase in pressure in the pulmonary circulation incidental to left-sided failure inevitably burdens the right side of the heart. The cause of right-sided heart failure must then include all of those that induce left-sided heart failure. Pure right-sided heart failure is infrequent and usually occurs in patients with any one of a variety of disorders affecting the lungs; hence, it is often referred to as corpulmonale. Corpulmonale is most commonly associated with parenchymal diseases of the lung, but can also arise secondary to disorders that affect the pulmonary vasculature (e.g., primary pulmonary hypertension), recurrent pulmonary thromboembolism, or that merely produce hypoxia (e.g., chronic sleep apnea, altitude sickness) , with is associated pulmonary vasoconstriction. The common feature of these divers disorder is pulmonary hypertension (discussed later), which result in hypertrophy and dilation of the right side of the heart. In extreme cases, leftward bulging of the ventricular septum can cause left ventricular dysfunction. The major morphologic and clinical effects of right-sided heart failure differ from those of left-sided heart failure in that pulmonary congestion is minimal, whereas engorgement of systemic and portal venous systems may be pronounced.