Implantable cardioverter defibrillator (ICD) has been shown to be associated with a significant reduction in the risk of sudden cardiac death. The aim of this study was to assess the prevalence and to identify the clinical predictors of appropriate ICD therapy in patients with chronic heart failure following implantation of an ICD for primary prevention. A monocenter retrospective analysis was performed and all consecutive patients undergoing implantation of ICD for primary prevention were included. Device interrogations were performed and appropriate therapies were recorded. The endpoint follow-up was the last available device interrogation in our center. Of 317 primary prevention patients undergoing ICD implantation, 203 (64%) had ischemic cardiomyopathy (ICM) and 114 had non-ischemic dilated cardiomyopathy (NIDCM). After a mean follow-up time 760±599 days, 56 (17.7%) had received appropriate ICD therapies. Mean LVEF was 26±6%. By univariate comparison, LVDD≥65mm(p=0.035) and lack of diuretic (p=0.024) were predictors for ICD therapy. Absence of cardiac resynchronization therapy device (CRTD) was close to be significant (p=0.055). ICM and NIDCM patients benefit from ICD implantation did not differ (p=0.941). By multivariate analysis, elderly patients≥65y (HR 1.92, p=0.032), LVDD≥65mm(HR 2.01, p=0.022) and lack of diuretic (HR 0.31, p<0.001) were all significant independent predictors for ICD therapy. Overall, the absence of CRTD device was close to be significant (H 0.53, p=0.062), but was significant in NIDCM population (p=0.007). During follow-up, the onset of atrial fibrillation (p=0.027) and hospitalization for acute heart failure (p=0.002) were significantly associated with ICD-delivered therapy. ICD therapy occurred in 17.7% of primary prevention patients without any difference between ICM and NIDCM. Older age, LV dilatation and absence of diuretic were predictive factors for ICD therapy. Presence of CRTD was close to be significant (figure next page).