Eighteen men with myocardial infarction in their history and without signs of heart failure were investigated at rest and during standard supine exercise. In nine patients aneurysma or diskinesis of the left ventricular wall were found. The left ventricular end-diastolic volume was determined from the wash-out of 133Xe injected into the left ventricle by means of precordial scintillation counting. During exercise the cardiac index rose owing to acceleration of the heart rate, whereas the stroke index remained unchanged, and the left ventricular work and stroke indices increased. The left ventricular end-diastolic pressure, elevated at rest, reached high values during exercise. The left ventricular end-diastolic and residual volumes decreased during exercise in most patients, and simultaneously the systolic ejection fraction increased. In patients with aneurysma or diskinesis the end-diastolic volume both at rest and during exercise does not differ from EDV of other patients. Six patients developed angina pectoris during exercise, but their haemodynamics did not differ significantly. It is concluded that the left ventricle in patients with advanced coronary heart disease and previous myocardial infarction shows the signs rather of diminished compliance than of heart failure during adequate exercise and still possesses some functional reserves.