['Cardiac resynchronization therapy (CRT) can result in profound reverse remodelling. The goal of this study was to identify factors predictive of such beneficial response.', 'Super-response to CRT was defined as normalization or near normalization of left ventricular systolic function without recognized reversible causes of heart failure. In a retrospective study, we compared baseline demographic, electrocardiogram, and echocardiographic characteristics of super-responders (n = 21) with a population of unselected consecutive cardiac CRT patients (Control 1, n = 330) and another sex-, age-, and aetiology-matched control group (Control 2, n = 43). Compared with Control 1, super-responders had significantly smaller left ventricular end-diastolic diameter (65.4 ± 6.4 vs. 73.4 ± 9.3 mm, P = 0.0001), higher ejection fraction (0.25 ± 0.05 vs. 0.22 ± 0.04, P = 0.004), smaller degree of mitral regurgitation (MR; mean value 1.9 ± 0.9 vs. 2.6 ± 0.8, P = <0.0001), and smaller left atrium (LA; 42.8 ± 4.6 vs. 50.0 ± 6.5 mm, P < 0.0001). Septal flash and inter-ventricular mechanical dyssynchrony were both more frequent among super-responders than in Control 2 subjects (93.8 vs. 69.8%; P = 0.01, and 93.8 vs. 62.8%; P = 0.01, respectively). In a multivariate analysis, smaller LA diameter and milder MR remained independent predictors of super-response.'] Do small left atrium and mild mitral regurgitation predict super-response to cardiac resynchronization therapy?