The effects of chronic volume and pressure overload on the heart will be studied in dogs in which a surgical lesion is produced in the circulation to produce an overload state. The resultant left ventricular hypertrophy will be examined from the standpoint of mechanical function with use of high speed cine ventriculography and computer image processing, and from the standpoint of blood flow and oxygenation with use of the radioactive microsphere method for blood flow measurement combined with coronary arterio-venous oxygen difference. Correlation of systolic function, diastolic elasticity, blood flow, blood flow distribution and oxygen consumption will be made to determine the factors which cause reduced function in the hypertrophied heart.