['We evaluated the ability of delayed enhancement magnetic resonance imaging (DE-MRI) to predict clinical response to cardiac resynchronization therapy (CRT).', 'Cardiac resynchronization therapy reduces morbidity and mortality in selected heart failure patients. However, up to 30% of patients do not have a response. We hypothesized that scar burden on DE-MRI predicts response to CRT.', 'The DE-MRI was performed on 28 heart failure patients undergoing CRT. Patients with QRS > or =120 ms, left ventricular ejection fraction < or =35%, New York Heart Association functional class II to IV, and dyssynchrony > or =60 ms were studied. Baseline and 3-month clinical follow-up, wall motion, 6-min walk, and quality of life assessment were performed. The DE-MRI was performed 10 min after 0.20 mmol/kg intravenous gadolinium. Scar measured by planimetry was correlated with response criteria.', 'Twenty-three patients completed the protocol (mean age 64.9 +/- 11.7 years), with 12 (52%) having a history of myocardial infarction. Thirteen (57%) patients met response criteria. Percent total scar was significantly higher in the nonresponse versus response group (median and interquartile range of 24.7% [18.1 to 48.7] vs. 1.0% [0.0 to 8.7], p = 0.0022) and predicted nonresponse by receiver-operating characteristic analysis (area = 0.94). At a cutoff value of 15%, percent total scar provided a sensitivity and specificity of 85% and 90%, respectively, for clinical response to CRT. Similarly, septal scar < or =40% provided a 100% sensitivity and specificity for response. Regression analysis showed linear correlations between percent total scar and change in each of the individual response criteria.'] Does delayed enhancement magnetic resonance imaging predict response to cardiac resynchronization therapy in patients with intraventricular dyssynchrony?