Twenty-four mongrel dogs were divided into two equal groups to determine the effects of orally administered amiodarone on left ventricular function. Measurements of left ventricular function included left ventricular contractility as denoted by maximum rate of rise of left ventricular pressure (dP/dtmax), cardiac index (CI), left ventricular stroke work index (LVSWI), and peripheral vascular resistance (PVR). Left ventricular function was measured in 6 of the 12 animals in Group 1 before and after 14 days of amiodarone administered orally; the remaining animals served as controls. The dP/dtmax was reduced from 2,855 to 1,291 mm Hg/sec (p less than 0.01), and LVSWI fell from 1.6 to 0.74 gm-m/beat/kg (p less than 0.05) in the 6 animals given amiodarone. The 12 animals in Group 2 underwent 30 minutes of ischemic arrest. Six animals in Group 2 underwent 30 minutes of ischemic arrest. Six animals were given amiodarone orally for 14 days prior to cardiopulmonary bypass and ischemic arrest; the other 6 served as controls. Before cardiopulmonary bypass, the dogs administered amiodarone had significantly greater depression of dP/dtmax (p less than 0.01) and LVSWI (p less than 0.05). Thirty minutes of ischemia produced significant depression of left ventricular function in all animals in Group 2. However, a significantly greater reduction in dP/dtmax and LVSWI occurred in those animals receiving amiodarone. Furthermore, 4 of the 6 dogs receiving amiodarone were unable to sustain sufficient cardiac output following cardiopulmonary bypass to permit long-term survival (p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)