Ventricular tachycardia and ventricular fibrillation are recognized complications of cardiac catheterization. Despite numerous reports documenting the frequency of these occurrences, their significance has not been systematically examined. Accordingly, the outcome of 108 patients who experienced either ventricular tachycardia or ventricular fibrillation during coronary angiography between 1975 and 1979 in the Coronary Artery Surgery Study (CASS) Registry were examined. There were 20, 142 patients analyzed. Patients with ventricular tachyarrhythmias had more objective evidence of left ventricular impairment, clinical heart failure, and ventricular arrhythmia recorded as a clinical symptom. The overall 5-year survival rates were 83% and 88% for patients with and without ventricular tachyarrhythmias, respectively (p=0.07). When ventricular function, age, gender, angina, and previous myocardial infarction were added in a stepwise Cox survival analysis, the presence of arrhythmias was not significant (p=0.66). At 5 years, 80% of the medically treated patients and 82% of the surgically treated patients remained alive (p=0.95). The only statistically significant differences in the patients with ventricular arrhythmias who were treated medically or surgically were age (medically treated patients 52±10 years, surgical patients 57±9 years, p=0.01) and number of diseased vessels (p<0.001). In a stepwise Cox survival analysis, functional impairment secondary to congestive heart failure was the only significant covariate to affect survival in the medical and surgical groups (p=0.0001). Surgical therapy itself was not significant (p=1.00). The incidence of sudden death during 5 years for patients with and without ventricular tachyarrhythmias during catheterization was 5% and 4%, respectively (p=0.28). None of the 29 patients with ventricular tachyarrhythmias who did not have coronary artery disease experienced sudden death. In the 79 patients with coronary artery disease, the 5-year incidence of sudden death was 19% in the patients with functional impairment due to congestive heart failure and 4% in the patients without functional impairment due to congestive heart failure (p=0.05). For patients with arrhythmias who were candidates for bypass surgery, there were no sudden deaths among the surgical patients. However, 14% of the medically treated patients had sudden death within 5 years (p=0.03). Thus, these data indicate that the occurrence of ventricular tachyarrhythmias occurring in the absence of myocardial infarction during cardiac catheterization does not confer an adverse prognosis. Rather, prognosis is governed by the presence or absence of coronary artery disease and the degree of left ventricular dysfunction. © 1990.