Ventricular arrhythmia and left ventricular dysfunction after hospital discharge in acute myocardial infarction are powerful predictors of sudden death. We evaluated the ventricular extrasystoles with 24 hour ambulatory electrocardiography at convalescent phase in 34 patients of acute myocardial infarction. Ventricular extrasystoles were observed in 19 patients (56%) and classified by Lown's grading system as grade 1 for 8 cases, grade 2 for 3 cases, grade 3 for 3 cases, grade 4 for 3 cases, and grade 5 for 2 cases. There was no relation between the develoment of ventricular extrasytoles and the risk factors of ischemic heart discase such as smoking, hypertension, hyperlipidemia, diabetes mellitus, and male sex. Also, the development of ventricular extrasystoles was independent to infarct site, regional wall motion abnormalities, and clinical manifestations of left ventricular dysfunction such as congestive heart failure and cardiomegaly. In conclusion, ventricular arrhythmia might independently predict the prognosis in survivors of acute myocardial infarction.