Argatroban is increasingly used in patients with heparin-induced thrombocytopenia. Although the recommended activated clotting time during percutaneous coronary intervention is 300-450 s, this recommendation is based on the limited data. This single-center, retrospective study evaluated the efficacy (composite of death, myocardial infarction, or urgent revascularization) and safety (evaluated by thrombolysis in myocardial infarction major bleeding) of argatroban during percutaneous coronary intervention according to activated clotting time levels. Patients were divided into three groups according to the activated clotting time achieved during the procedure (<300s, 300-450s, and >450 s). In this study, 120 consecutive patients with confirmed or suspected heparin-induced thrombocytopenia received argatroban (241 +/- 104 mug/kg bolus, followed by a 18 +/- 10 microg/kg per min infusion) during percutaneous coronary intervention. The indication for percutaneous coronary intervention was stable angina in 20% of patients, unstable angina or non-ST elevation myocardial infarction in 58%, and ST elevation myocardial infarction in 22%. An adjunctive glycoprotein IIb/IIIa inhibitor was used in 56 patients (46.7%). When divided into three groups on the basis of the activated clotting time (<300, 300-450, >450 s), no significant difference was observed between the groups in the efficacy endpoint, which occurred in 9.8% (6/61) of patients in the group with activated clotting time less than 300 s, 19.6% (9/46) of patients in the group with activated clotting time 300-450 s, and 7.7% (1/13) of patients in the group with activated clotting time more than 450 s (P = 0.58). The rate of major bleeding was higher in the group of patients with activated clotting time more than 450 s (1.6, 0, and 15.4% patients, respectively; P = 0.006). These results suggest that in patients undergoing percutaneous coronary intervention, argatroban provides adequate anticoagulation with a low bleeding rate, when activated clotting time is maintained below 450 s.