Nineteen patients with chronic cor pulmonale, in which the coincidence with other cardiovascular disease was excluded by cardiac catheterization and coronary arteriography, were examined. Left ventricular hypertrophy, elevated filling pressure and reduced compliance were found in a part of the patients. The left ventricular ejection fraction was normal and had no correlation with the elevated filling pressures. These abnormalities were related to the degree of pulmonary hypertension; furthermore, the correlation between the left ventricular hypertrophy and reduced compliance has been found. The author concludes that chronic obstructive bronchopulmonary disease is not accompanied by left ventricular contractile insufficiency; the left ventricle is able to develop a normal systolic performance at rest. In a part of patients, however, this systolic performance is developed at certain abnormal haemodynamic conditions, particularly at elevated left ventricular filling pressure. Possible mechanisms responsible for these alterations are discussed.