Paroxysmal supraventricular tachycardia (PSVT) is a reentrant tachycardia, and the autonomic nervous system influences the paroxysms of PSVT. Tofisopam (Grandaxin) is a derivative of benzodiazepines. It is reported that heart rate variability (HRV) reveals the function of the autonomic nervous system and is used as an index of the effects of the autonomic nervous system on the heart rhythm. In previous studies, it was reported that tofisopam improved HRV. In this case report, the frequency of PSVT was significantly decreased and subjective symptoms of arrhythmia were eliminated after the administration of tofisopam. R-R interval variability and high-frequency power (HF; 0.15-0.40 Hz) were increased, and [low-frequency power (LF; 0.04-0.15 Hz)]/HF was decreased after administration of tofisopam. These results suggest that tofisopam overcame the existing imbalance of the sympathetic and vagus nervous system. In this case report, it is suggested that tofisopam is effective for the treatment of PSVT.