Frequent or repetitive ventricular premature complexes (VPCs) occurring soon after acute myocardial infarction are predictors of subsequent mortality independent of left ventricular dysfunction. The Cardiac Arrhythmia Pilot Study (CAPS) is a 10-center study sponsored by the National Heart, Lung, and Blood Institute to determine whether postinfarction ventricular arrhythmias can be satisfactorily reduced for 1 year after acute myocardial infarction. Patients younger than 75 years are screened for arrhythmias 6 to 60 days after acute myocardial infarction. To qualify for CAPS, patients must have at least 10 VPCs or at least 5 runs of 3 to 9 consecutive VPCs in a 24-hour electrocardiographic recording and a left ventricular ejection fraction greater than 0.20. Eligible patients without exclusion criteria are randomized into 1 of 5 treatment tracks (4 active treatment and 1 placebo). Within a treatment track, patients are permitted to change drug and dosage in order to achieve at least 70% reduction in VPC frequency and at least 90% reduction in runs of VPCs over 1 year of follow-up. In addition to efficacy assessment, adverse effects, particularly proarrhythmic effects, are being monitored. The results in CAPS will be pivotal for deciding whether a fullscale trial to determine whether controlling ventricular arrhythmias will reduce mortality risk is feasible.