The number of patients with cardiac arrhythmias is increasing in our society with the aged people along with hypertension, diabetes mellitus, metabolic syndrome and ischemic heart diseases. Patient characteristics and therapeutic tools are both diverse at present, and, therefore, clinical evidence is one of the important pieces for selecting therapy suitable for our individual patients. This article reviews recent clinical trials regarding to atrial fibrillation and ventricular tachycardia/fibrillation. We have many powerful knowledge and tools, but at the same time, know well some limitations peculiar to individual therapy for particular arrhythmias.