There is a need for effective, well-tolerated antiarrhythmic agents, particularly those effective by both intravenous and oral routes. Lorcainide, a new antiarrhythmic drug with such properties, was given long-term orally to 24 patients controlled initially with intravenous therapy--19 with frequent (greater than 1/min) complex premature ventricular complexes (PVCs) on a baseline 24-hour Holter monitor and five with ongoing sustained ventricular tachycardia (VT) or frequent paroxysmal sustained VT, for a mean of 13 months (range 0.03 to 39.4 months). Long-term lorcainide was given in divided doses of 200 to 800 mg/day (median 260, mean 269 +/- 90 mg/day). Response to long-term lorcainide therapy was assessed at a mean of both 26 days and 12.2 months. Frequency of PVCs on baseline averaged 13,490/24 hours (median 10,578, range 2,115 to 61,716); couplets averaged 309/24 hours (median 166, range 0 to 5,686), and runs averaged 33/24 hours (median 30, range 0 to 2,951). Median frequency of PVCs decreased by 94% (p much less than 0.001) and 97% (p less than 0.01) at the first and second lorcainide efficacy assessments, respectively. Couplets decreased by a median of 99% (p much less than 0.001) and 100% (p less than 0.005) at the first and second assessments, respectively. Runs were suppressed by a median of 100% at both evaluations (p much less than 0.001). Only three (16%) of the patients with complex PVCs failed to respond to therapy. No recurrence during lorcainide has been noted in the five patients with ongoing sustained VT or recurrent episodes of VT.(ABSTRACT TRUNCATED AT 250 WORDS)