We examined the role of electrophysiologic testing in the prediction of long-term outcome in 166 survivors of out-of-hospital cardiac arrest not associated with acute myocardial infarction. Ventricular arrhythmias were inducible in 131 patients (79 percent) at base line and were suppressed by antiarrhythmic drugs or surgery (or both) in 91 of 127 (72 percent). During a median follow-up period of 21 months, cardiac arrest recurred in 29 patients: 11 (12 percent) of the 91 in whom inducible arrhythmias had been suppressed (including 5 patients in whom treatment had been discontinued), 12 (33 percent) of the 36 in whom inducible arrhythmias persisted, and 6 (17 percent) of the 35 in whom arrhythmias could not be induced at the initial electrophysiologic study. Cox survival analysis identified the following three variables as significant independent predictors of recurrent cardiac arrest: persistence of inducible ventricular arrhythmias (relative risk, 3.97 [95 percent confidence interval, 1.80 to 8.75], P = 0.0006), a left ventricular ejection fraction of 30 percent or less (relative risk, 2.60 [1.21 to 5.53], P = 0.0138), and the absence of cardiac surgery (relative risk, 4.20 [0.99 to 17.77], P = 0.0512). We conclude that electrophysiologic testing is useful in quantifying the subsequent risk of cardiac arrest among survivors of out-of-hospital cardiac arrest.