Background: In the present study, we examined the predictors of outcome of 103 patients with coronary artery disease and left ventricular dysfunction who had life-threatening ventricular arrhythmias and were treated with implantable cardioverter-defibrillators with the use of single-photon emission computed tomography (SPECT). Methods and Results: During a mean follow-up of 29 months, there were 29 cardiac deaths. In comparison with patients who died, survivors had less diabetes mellitus (45% versus 19%, P<.007), higher left ventricular ejection fraction (23±9% versus 27±11%, P=.04), and fewer perfusion defects as determined with stress SPECT (15±5 versus 12±5, P<.004). Most of the perfusion defects were fixed, indicative of scarring; the extent of reversible defects did not differ (2±3 in survivors and 3±4 in nonsurvivors). Multivariate Cox survival analysis identified the number of fixed defects as the only independent predictor of death (χ2=10, P=.002). There were six deaths among 42 patients (14%) with <8 fixed defects compared with 23 deaths among 61 patients (38%) with ≤8 defects (P=.005). The 4-year survival was better in patients with <8 segmental fixed defects than in those with >8 fixed defects (80% versus 36%) (χ2=8, P=.005). Conclusions: The myocardial perfusion pattern is an important determinant of outcome in patients with life-threatening ventricular arrhythmias who are treated with a implantable cardioverter- defibrillator. The extent of scarring separates patients into high- and low- risk groups with a 2.7-fold difference in death rate.