In a randomized prospective study 32 patients received either alinidine or a placebo for the first five postoperative days after coronary bypass surgery. The purpose of the study was to investigate the prophylactic antiarrhythmic properties of alinidine on supraventricular tachyarrhythmias (svt), which occur with incidence after open heart surgery. There was no significant difference in pretherapeutical parameters between the two groups. Eleven out of sixteen control patients (69%) and none of the patients treated with alinidine had svt. All arrhythmias occurred in the first three postoperative days and required medical treatment. Even after alinidine was stopped, patients in this group did not experience arrhythmias. The mean systolic blood pressure in the treatment group was 113 +/- 13 mmHg, in the control group it was 119 +/- 16 mmHg. The mean heart rate tended to be lower in the alinidine group (82 +/- 12 beats min-1 91 +/- 21 beats min-1. In 1/16 patients the alinidine treatment was stopped due to marked hypotension (less than 90 mmHg) and bradycardia (less than beats min-1). Two other patients in this group had short periods of mild bradycardia (less than 60 beats min-1) which was tolerated well. Additional medical treatment was not needed. In this study prophylactic treatment with alinidine proved to be highly effective in preventing postoperative arrhythmias following myocardial revascularisation.