Propafenone (P), a class IC antiarrhythmic drug, was tested intravenously and orally in the curative and preventive treatment of sustained (VTS) and non-sustained (VTNS) ventricular tachycardia. The 16 patients involved included 11 men and 5 women of mean age 49 years. They all had heart disease: ischaemia in 3, right ventricular arrhythmogenic dysplasia in 6, dilated myocardiopathy in 5 and left ventricular aneurysm in 2. Intravenous P in doses of 1.5 mg/kg controlled VT within 2 or 3 minutes on average in 9 out of 12 patients. Following the injection VT could not be reinduced in 2 out of 10 patients; other inductions were harder to obtain or resulted in VTNS instead of VTS (n = 3), or remained unchanged (n = 5). When P was administered orally (mean dose 900 mg) to 14 patients reinduction of VT was no longer possible in 2 cases, more difficult in 1 case, remained unchanged in 7 cases and was easier in 4 cases. Long-term oral therapy at the same dosage level prevented recurrences of VT in 7 out of 14 patients; the drug was discontinued in 2 patients owing to its arrhythmogenic effect on induced VT. The patients were followed up for 5 to 36 months (mean: 16.4 +/- 11.7 months). In this trial the results of long-term treatment could not be predicted from Holter recordings or measurements of plasma levels.(ABSTRACT TRUNCATED AT 250 WORDS)