Tiapamil was effectively used in 32 surgical patients in the treatment of intra-and postoperative cardiac arrhythmias such as atrial fibrillation, supraventricular paroxysmal tachycardia and extrasystoles and in ventricular ectopic beats. In 28 patients aged between 38 and 82 years, bolus doses of 0.3-1.5 mg/kg were used. Before administration, hypoxaemia, hypercarbia, metabolic acidosis and electrolyte imbalances were excluded. Small doses of 0.3-0.5 mg/kg were only effective in patients with tachycardic atrial fibrillation. In most other arrhythmias the effective dose was between 1 and 1.5 mg/kg. In 4 surgical patients aged between 56 and 82 years, the continuous infusion of 12-25 mg/h (in 2 patients preceded by a bolus injection of 1 mg/kg) was effective in abolishing arrhythmias. In 18 healthy subjects, systolic time intervals were measured continuously and noninvasively before, during and for 9 min after 1 mg/kg tiapamil or 0.13 mg/kg verapamil, given intravenously according to a randomization schedule. Heart rate increased and systolic blood pressure decreased slightly but significantly. A significant improvement in myocardial function, with a decrease in PEP and PEP/LVET ratio, was found after both calcium antagonists. The effect of tiapamil on myocardial function lasted significantly longer than that of verapamil.