We investigated the vasodilating effect of diltiazem on basal as well as digoxin-dependent splanchnic and systemic hemodynamics in 12 normotensive men, using the hepatic venous catheter technique, the thermodilution method and systolic time intervals. After baseline measurements, diltiazem was administered by a primed-constant infusion (2.5 micrograms/kg/min) in 6 out of 12 subjects. Following an equilibration period of diltiazem infusion, 1 mg digoxin was infused concomitantly over 15 min and hemodynamic changes were determined over 105 min. Control trials with digoxin and concomitant saline infusion were also performed in 7 out of 12 subjects. Diltiazem medication alone lowered only systolic blood pressure without affecting splanchnic hemodynamics. Digoxin without comedication provoked an increase in systolic blood pressure, a decrease in heart rate, mean pulmonary artery pressure and total electromechanical systole (positive inotropic effect), and significantly reduced splanchnic blood flow and increased splanchnic vascular resistance. During concomitant diltiazem infusion, digoxin did not alter splanchnic hemodynamics while the shortening of total electromechanical systole remained unchanged. We conclude, that diltiazem attenuates digoxin-induced splanchnic vasoconstriction and therefore, might be useful in the treatment of digitalis-dependent splanchnic vascular insufficiency.