The effects of constant-infusion verapamil were studied in ten postoperative ICU patients who developed supraventricular tachycardia (atrial fibrillation) with rapid ventricular response rates. A 5-mg iv bolus dose of verapamil was followed by a 5-mg/h infusion that continued for 8 h. Ventricular rates were significantly (p less than .005) reduced from a pretreatment mean of 156 +/- 14 (SD) to 104 +/- 9 beat/min on constant-infusion therapy. This therapy was well tolerated without observed side-effects. Moreover, constant-infusion verapamil might avoid the hypotension and wide range of ventricular rates frequently encountered with repeated bolus doses of verapamil.