Previous reports of cor pulmonale due to upper airway obstruction have not noted that chronic hypoxemia due to alveolar hypoventilation can lead to left as well as right ventricular failure in these patients. We found elevated left ventricular end-diastolic pressure in four of five patients. Although these patients have frequent respiratory infections, no investigation of their immune status has previously been reported. We performed such investigations but could not demonstrate an immunologic deficiency. Although nine of 44 patients previously reported were mentally retarded, no psychometric data were available. We studied five patients but could not determine the role of mental subnormality in this syndrome. Diagnosis of this syndrome should be suspected when clinical and roentgenographic findings of biventricular heart failure are associated with right ventricular hypertrophy on electrocardiogram. The diagnosis of alveolar hypoventilation is confirmed by blood gas findings and examination of the upper airways. Surgical removal of obstructive tissue reverses the cardiac involvement.