Introduction: Digitalis use in patients with severe heart failure is controversial. We assessed the effects of digitalis therapy on mortality in a large, observational study in recipients of cardiac resynchronization therapy (CRT). Methods: Consecutive patients receiving a CRT-defibrillator in three European tertiary referral centers were enrolled and followed for a median of 28 months. Digitalis use was assessed at the time of CRT implantation. Multivariate Cox-regression model and propensity score matching was used to determine all-cause mortality as primary endpoint. CRT-response (defined as improvement of ≥1 NYHA class), echocardiographic improvement (defined as improvement of LVEF of ≥ 5%), and ICD shocks were assessed as secondary endpoints. Results: The study comprised 552 CRT recipients with standard indications, including 219 patients (40%) treated with digitalis. Compared to patients without digitalis, they had more often atrial fibrillation, poorer LVEF and higher NYHA class (all p ≤ 0.002). Crude analysis of all-cause mortality demonstrated a similar relative risk of death for patients with and without digitalis (HR=1.14; 95% CI 0.88-1.5; p=0.40). After adjustment for independent predictors of mortality, digitalis therapy did not alter the risk for death (adjusted HR=1.04; 95% CI 0.75-1.45; p=0.82). Also, in comparison to 286 propensity score matched patients, mortality was not affected by digitalis intake (propensity adjusted HR=1.11; 95% CI 0.72-1.70; p=0.64). CRT response was predominant in digitalis non-users concerning both improvement of HF symptoms and LVEF (NYHA p<0.01; LVEF p<0.01) while patients on digitalis had more often ventricular tachyarrhythmias requiring ICD shock (p=0.01). Conclusions: Digitalis therapy had no effect on mortality but did negatively affect CRT response and susceptibility to ventricular arrhythmias requiring ICD shock treatment.