Mapping of the unorganized activation patterns of atrial fibrillation requires a high-resolution mapping approach to diagnose substrate-mediated pathophysiological mechanisms. At present, epicardial mapping is the only approach that is able to acquire electrograms of >200 high-density sites simultaneously. This study introduces a technique to perform high-resolution mapping in minimally invasive surgery. In 3 patients with mitral valve disease, epicardial mapping of the right atrium, Bachmann's bundle and parts of the left atrium was safely performed via minimal right thoracotomy.