Hepatic vascular complications are major causes of graft loss and mortality after orthotopic liver transplantation (OLT). Measures like pharmacologic prophylaxis might reduce the risk of these complications. This prospective, randomized, double-blind study evaluated the effects of perioperative diltiazem infusion on blood flow rates in vessels of transplanted liver grafts. Eleven patients who underwent living-related OLT between December 2003 and June 2004 were studied in two groups. One group (Group D, n=5) received diltiazem 1 µg/kg/min for 24 hrs postoperatively. The control group (Group C, n=6) received an infusion of normal saline for this period. Each subject’s demographic data; postoperative serum levels of aspartate aminotransferase, alanine aminotransferase, total cholesterol, and bilirubin; and postoperative prothrombin time and partial thromboplastin time were recorded. As well, Doppler ultrasonography was used to measure blood flow parameters in the hepatic artery, portal vein, and hepatic vein at the completion of vascular anastomosis and on postoperative day 1. Hemodynamic parameters (systolic, diastolic, and mean arterial pressure) were also recorded. The groups were similar with respect to demographic features and postoperative laboratory results. Compared with baseline, in Group D findings for peak systolic velocity in the hepatic artery and portal vein on postoperative day 1 revealed increases of 38% and 51%, respectively (hepatic artery 53 ± 17 vs 68 ± 24 cm/s; portal vein 49 ± 34 cm/s vs 95 ± 60 cm/s). The corresponding peak systolic velocity changes in Group C were decreases of 12% and 22%, respectively (hepatic artery 100 ± 52 vs 77 ± 45 cm/s; portal vein 109 ± 59 vs 85 ± 23 cm/s). However, the only significant change was the increase in portal vein flow rate in Group D (p<0.05). This preliminary result suggests that perioperative diltiazem infusion may increase hepatic artery blood flow after OLT. However, the clinical implications of this finding relative to reducing the risk of graft vascular complications after OLT remains to be determined in larger studies.