One of the main areas of interest in interventional cardiology is the understanding, and ultimate prevention of restenosis after an initially successful percutaneous transluminal coronary angioplasty. Restenosis is the recurrence of luminal narrowing following angioplasty, and still frustrates the late results in the treatment of angina pectoris. Experimental, pathological and clinical studies suggest that restenosis may occur via activation of the coagulation cascade, platelet activation and thrombus formation. Thrombin itself is identified as the most potent platelet activator, and has a pivotal role in the coagulation system. Furthermore, thrombin directly mediates smooth muscle cell proliferation by stimulating thrombin receptors at the smooth muscle cell surface. Thrombus indirectly induces excessive intimal smooth muscle cell proliferation by means of released mitogens (growth factors), which may contribute to late restenosis. Therefore direct and irreversible thrombin blockade by hirudin is deemed to be effective in the prevention of restenosis following angioplasty. The HELVETICA trial is a multicentre, randomized, double-blind heparin-controlled study, designed to compare the effects of two dose regimens of recombinant-hirudin (CGP 39,393/TMRevasc) with those of heparin on event-free survival, safety, tolerability and luminal renarrowing using quantitative coronary angiography no later than 26 weeks after the coronary angioplasty procedure.