The effect of acetyl-strophanthidin, a rapidly acting digitalis-like drug, was measured on peak flow velocity, stroke distance (an index of stroke volume) and minute distance (an index of cardiac output), determined by Doppler echocardiography in 21 subjects with a wide range of left ventricular ejection fractions (12 to 89%, average 47%). For the total study group, peak flow velocity increased from 99 +/- 10 to 110 +/- 13 cm/s (p less than 0.01), and stroke distance increased from 15.1 +/- 3.2 to 16.8 +/- 3.1 cm (p less than 0.01). Minute distance remained unchanged: 1,093 +/- 168 cm before and 1,129 +/- 187 cm after acetyl-strophanthidin (difference not significant). Improvement in Doppler parameters of forward blood flow was significantly (p less than 0.001) greater in subjects with left ventricular ejection fractions less than 60% (+17% for peak flow velocity, +22% for stroke distance and +15% for minute distance) than those with left ventricular ejection fractions greater than or equal to 60% (+4% for peak flow velocity, +2% for stroke distance and -8% for minute distance). These data suggest that Doppler echocardiography is a useful method to assess the efficacy of acute digitalis administration in improving forward blood flow.