In two groups of healthy men the dynamics of left-ventricular contraction was studied by Weissler's method based on synchronous recording of ECG, phonocardiogram and carotid sphygmogram. Group I comprised 20 subjects in whom this recording was performed during maximal exercise and 90-minute restitution (1 W/kg/6 min, 2 W/kg/6 min, 3 W/kg/6 min). Group II (n = 17) performed the same exercise immediately after intravenous injection of glucagon 50 micrograms/kg of body weight. Glucagon administration before the exercise reduced the functional reserve of the left ventricle during the exercise impairing the pumping action of the left ventricle during the restitution. After glucagon administration the restitution of left-ventricular contraction periods was characterized by decreased value of the ejection time index (LVETI), prolonged pre-ejection period (PEP), isovolumetric contraction time (ICT), and diminished LVET/PEP index in relation to the values obtained at the same time in the control group (p less than 0.05). Glucagon caused no changes in the exercise tolerance of the studied subjects and had no effect on the time of postexercise restitution.