It behooves clinical investigators in a University Hospital group to survey from time to time, recorded clinical material on pressing diagnostic and therapeutic problems. Heart disease of pulmonary origin is a pertinent and pressing topic for, when fully developed, it has been considered hopeless by too many physicians. We have, therefore, reviewed our cases in an attempt to reemphasize precipitating and perpetuating conditions, determine predisposing factors and evaluate early diagnostic signs. We hope to touch upon possible prophylactic measures and argue for the establishment of as effective a program of management as possible. We first studied the records of 208 cases, who had been cross filed under the diagnosis of chronic cor pulmonale. It soon became apparent that minimal criteria for the diagnosis of chronic cor pulmonale had to be established, and after considerable study we arrived at those set down in Table I. We were acutely aware that chronic cor pulmonale is an end result of an insidious process. Furthermore we were fully conscious of the difficulty of arbitrarily drawing a line separating definite cor pulmonale from pulmonary disease with positional electrocardiographic changes. The application of our criteria, as outlined here, has limited our study to patients with definite respiratory disease and pulmonary hypertension, and definite right atrial and right ventricular enlargement; as shown by the electrocardiogram or the teleradiogram. In addition, we have accepted the presence of right heart failure, without left failure, as presumptive evidence of right ventricular enlargement, even when other signs were equivocal. Patients with tricuspid or pulmonary valvular