The presence of ventricular ectopic activity in the post-myocardial infarction patient, especially associated with left ventricular dysfunction, has been associated with a high incidence of sudden cardiac death. To test the PVC hypothesis, that PVC suppression in asymptomatic patients with ventricular arrhythmias post-myocardial infarction might reduce sudden death rate, the cardiac arrhythmia suppression trial (CAST) was performed. In patients treated with encainide or flecainide, total mortality at 10 months was 7.7% compared to only 3% overall mortality on placebo. The increase in mortality and sudden cardiac death with these two drugs raised the question of whether PVC suppression in this group of patients should be attempted. In addition, the extrapolation of the results of this study to other patient groups has resulted in a change of our antiarrhythmic prescription habits. Criticism of the CAST study has included a low placebo mortality, which may have been secondary to entry of low-risk groups of patients, deaths in the open label titration groups not being included, and recent advances in thrombolysis and revascularization. In addition, this low placebo mortality may have been explained by the concept that drug-responsive arrhythmias may have more benign prognosis. The above results suggest that, except for the use of beta blockers, benefits of other anti-arrhythmic drug treatment in the post-infarction patient with asymptomatic benign and potentially lethal ventricular arrhythmias is questionable. Flecainide and encainide should be avoided in this group of patients.(ABSTRACT TRUNCATED AT 250 WORDS)