Introduction: Cardiac resynchronization therapy (CRT) is an established treatment to improve left ventricular function in patients with heart failure with reduced ejection fraction, especially complete left branch block. However, the problem of non-response remains, and there is controversy regarding the best pacing site. Methods and Results: A 44-year-old patient with dilated cardiomyopathy underwent CRT. The epicardial polarity change site was paced and functional mitral regurgitation improved markedly owing to the synchrony of the papillary muscles compared with the other pacing site. Conclusion: Our findings suggest that this can be a new optimal left ventricular pacing site, considering the electrophysiological characteristics.