The effect of digitalis preparation on the normal heart has been the subject of controversy. Most of the studies using acute intravenous administration of digitalis or oral administration of its full dose demonstrated no positive effect on the normal heart. In subjects without congestive heart failure the positive inotropic action was probably masked by the increased peripheral vasoconstriction. In this study left ventricular performance was assessed mechanocardiographically and echocardiographically in ten normal non-trained subjects before and after oral administration of small dose of digoxin. Subjects and Methods Out of 100 non-trained healthy young males, ten subjects aged from 22 to 33 years were selected in whom a clear left ventricular echocardiograms could be contineously recorded at rest and during exercise. Echocardiogram (UCG), electrocardiogram (ECG), phonocardiogram (PCG) and blood pressure readings were obtained in the basal state and every one minute during 120 Watt steady state exercise of three minutes' duration in recumbent position before and after oral administration of digoxin, 0.5 mg on the first day and 1.0 mg on the subsequent day. The experimental procedures after digoxin treatment were done 4 hours after the second administration of digoxin. Blood pressure, the ratio of preejection period to ejection time (PEP/ET), percent shortening of left ventricular minor dimension (ΔD), ejection fraction (EF) and mean velocity of circumferential fiber shortening of the left ventricle (mVcf) were analyzed by the paired student's test comparing the control measures to the digoxin measures in the basal state, during and after exercise. Results Systolic and diastolic pressures were not affected by digoxin treatment. After digoxin administration, despite a decrease in heart rate from 67 ± 4 to 60 ± 5 in the basal state, PEP/ET decreased from 0.42 ± 0.05 to 0.38 ± 0.03 (p < 0.01), ΔD increased from 33 ± 4 to 38 ± 3% (p < 0.001), EF increased from 69 ± 6 to 76 ± 4% (p < 0.001) and mVcf increased from 1.20 ± 0.13 to 1.35 ± 0.11 (p < 0.01). During exercise, while a decrease in mean heart rate by digoxin treatment was as much as that of basal state, effects of digoxin therapy on ΔD and EF were augmented during exercise: ΔD increased from 34 ±4 to 44 ± 4% and EF increased form 71 ± 5 to 83 ± 4% at three minutes after initation of exercise. An increase in ΔD after digoxin treatment was mainly caused by a change in endsystolic dimension.