Primary hyperhidrosis has been associated with an increased activity of the sympathetic nervous system. Conventional nonsurgical therapies are inconvenient and only temporarily effective. Endoscopic thoracic sympathicotomy (ETS) is a minimal invasive procedure of thoracic sympathetic block and has been used successfully and safely in the treatment of primary palmar and axillary hyperhidrosis. Sympathicotomy results in an initial sympathovagal imbalance with a parasympathetic predominance, which is restored in a long-term basis. ETS is commonly performed to treat hyperhidrosis but there are some rare complications including cardiac arrest. In our hospital, we experienced 2 cases of patients who suffered from sudden cardiac arrest during right ETS, which was performed soon after left ETS. We're going to report these cases and consider about possible causes.