An echocardiographic study performed on 15 patients after administration of sublingual nitroglycerin showed a significant decrease in internal diameters of the left ventricle, associated with a moderate fall in blood pressure. A significant, but smaller decrease in diameters was also found 3 to 4 hours after oral administration of a nitroglycerin microcapsule preparation. The parameters measuring cardiac performance and the quality of myocardial contraction remained unchanged. The decrease in left ventricle internal diameters may be attributed to a reduction in pre-load and intraparietal ventricular tension. In addition, these results obtained by a non-invasive technique have confirmed the prolonged activity of nitroglycerin microcapsule preparations, previously demonstrated by hemodynamic and pharmacological experiments.