27 cardiac patients with a mean age of 58.5 years (S.D. +/- 9.43) were treated in the coronary care unit with tiapamil, a new Ca2+ antagonist, by intravenous infusion. The following arrhythmias were identified: ventricular premature complexes (VPCs, Lown class 3--5) in 15 patients, supraventricular premature complexes (SVPCs) in 6 patients, and mixed VPCs (Lown grade 5) plus SVPCs in 6 patients. ECGs and hemodynamic parameters were continuously monitored prior to, during and up to 24 hours after the therapy. In patients with VPCs, the median frequency of VPCs decreased from 612.0 to 64.0 at the 3rd hour of therapy (p less than 0.01). Between the 13th and the 24th hour after tiapamil, without therapy the median VPCs increased to 459.0. The median "VPCs/sinusal" beats ratio was decreased from 0.125 to 0.0108 (p less than 0.01) at the 3rd hour and returned to 0.1029 from the 9th to the 20th hour after stopping tiapamil. The results in the patients with SVPCs, or with VPCs + SVPCs were similar. Tiapamil did not affect the central venous pressure and decreased the median blood pressure from 130/80 to 110/75 mm Hg (p less than 0.10). The effects of tiapamil against all types of cardiac arrhythmias can therefore be defined as good. 1/27 patients presented hypotension that required therapy with dopamine, and mild subjective complaints (mainly headache) were reported in 6 patients. No complications occurred. The results show that tiapamil is effective both against SVPCs and VPCs, and thus its spectrum of action differs from that of other Ca2+ antagonists.