The current recommended weight-adjusted dosing regimen of unfractionated heparin and target activated clotting time (ACT) in percutaneous coronary intervention (PCI) is based on limited data from the western population, and the applicability in the various Asian ethnic groups remains unknown. This is a retrospective study in an Asian university teaching hospital. Among the 1287 patients who have undergone PCI, Chinese constituted 70.4% (n=906), Malay 15.5% (n=199) and Indian 14.1% (n=182). Overall, the mean total heparin dose was 6224+/-1548 U, mean weight-adjusted heparin dose was 95+/-30 U/kg, and mean ACT was 325+/-95 s. There was no significant difference in the 3 ethnic groups. Both the incidences of in-hospital ischemic complications (Chinese 2.4%, Malay 3.5%, Indian 2.2%, p=0.641) as well as in-hospital bleeding complications (Chinese 4.5%, Malay 3.5%, Indian 6.0%, p=0.490) were similar in the 3 ethnic groups. When the patients were divided based on ACT into 3 groups:<250, 250-350 and>350 seconds, the incidence of ischemic complication (2.5%, 2.5%, 2.7%) was similar (p=819), while that of bleeding complications (4.1%, 3.5%, 6.8%) showed a strong trend (p=0.057) of increased risk in patients with ACT>350 s. In conclusion, the recommended weight-adjusted heparin-dosing regimen in PCI derived from the western population is equally applicable to the Asian patients. ACT does not correlate with in-hospital ischemic complications, but increased bleeding complications were observed with ACT>350 s.