Indecainide, a new type Ic antiarrhythmic agent, and quinidine sulfate were compared in a randomized double-blind parallel study. Cardiac patients with greater than or equal to 30 ventricular premature complexes per hour hour received indecainide, 50 mg, or quinidine, 200 mg every 6 hours, and the doses were increased until more than 80% suppression was noted, adverse effects occurred or a maximal dose of 100 mg of indecainide or 400 mg of quinidine given every 6 hours. Efficacy was achieved in 8 of 10 taking indecainide (p less than 0.05) and 7 of 9 taking quinidine (p less than 0.05). At least 90% of episodes of ventricular tachycardia were suppressed in 4 of 7 patients taking indecainide and 1 of 4 taking quinidine. No adverse effects were observed in the 7 patients who responded to indecainide and the 4 who responded quinidine, resulting in short-term efficacy without adverse effects in 7 patients (70%) taking indecainide and 4 (44%) taking quinidine. The effective or maximal mean daily indecainide and quinidine doses were 190 +/- 32 mg and 1,022 +/- 291 mg, respectively; mean trough indecainide and quinidine concentrations were 617 +/- 247 ng/ml and 3.3 +/- 1.4 micrograms/ml, respectively. Indecainide prolonged mean PR and QRS intervals (p less than 0.05), but not QT and QTc intervals. Quinidine did not change PR or QRS intervals but prolonged QTc interval (p less than 0.05). During dosing, 1 patient discontinued indecainide treatment because of nausea; 3 discontinued quinidine because of gastrointestinal complaints.(ABSTRACT TRUNCATED AT 250 WORDS)