The effects of the molsidomine metabolite SIN-I (0.5 mg) on tolerance to ischemia were studied in twelve patients during coronary angioplasty of the LAD. SIN-I resulted in a significant prolongation of time to ST-segment alteration one, five and ten minutes after intracoronary injection. Beside hemodynamic reasons the effects of SIN-I on circulating blood cells and collateral perfusion are discussed as mechanisms of action. The effects of molsidomine (2 X 8 mg/d) on restenosis rate after initially successful coronary angioplasty were studied in 393 patients in a prospective, randomized and controlled trial. 29% of patients treated with molsidomine experienced restenosis at control coronary angiography at six months. The control group receiving nifedipine (3 X 20 mg/d) and acetylsalicylic acid (1 X 500 mg/d) showed a restenosis in 33% of patients. Therefore, molsidomine seems as effective as nifedipine and acetylsalicylic acid in treating patients after coronary angioplasty.