We investigated in 136 consecutive patients with heart failure receiving cardiac resynchronization therapy (CRT) the effect of carvedilol versus metoprolol CR/XL versus no beta blocker on mortality. Of the 136 patients, 42 (31%) were on carvedilol, 80 (59%) were on metoprolol CR/XL, and 14 (10%) were not on a beta blocker. A decrease of left ventricular end-systolic volume ≥15% after CRT was defined as a positive response to CRT. Of the 136 patients, 62 (46%) responded to CRT. It was found that both carvedilol and metoprolol CR/XL were not related to CRT response on using Cox univariate regression analysis. Twenty-two of the 136 patients (16%) died during follow-up of 17 ± 10 months after initiating CRT. Mortality occurred in 14 of 80 patients (18%) on metoprolol CR/XL, in 3 of 42 patients (7%) on carvedilol, and in 5 of 14 patients (36%) not on beta blockers (P = 0.04). After adjustment for age, gender, and the variables with significant differences by Cox univariate regression, both carvedilol (hazard ratio = 0.14; P = 0.03; 95% confidence interval = 0.02-0.86) and metoprolol CR/XL (hazard ratio = 0.19; P = 0.02; 95% confidence interval = 0.04-0.80) were found to be related to mortality by Cox multivariate regression.