Abstract: AIM:To investigate the role of cardiac deacetylase SIRT3 in ischemia/reperfusion (IR)-induced arrhythmias. METHODS: Twenty-four Sirt3 knockout (SIRT3 KO) mice and 24 wild-type (WT) mice were randomized into control group (Control, n=6), sham group (Sham, n=6), ischemia reperfusion group (I/R, n=6) and NAD+ treated I/R group (I/R+NAD, n=6). Wild-type and knockout mice were subjected to I (30 min)/R (2 h) and ECG was examined during I/R. NAD+ treatment was performed by intraperitoneal injection (7 days, 1 mg/kg/day) before I/R. At the end of the reperfusion period, arrhythmia score, reactive oxygen species (ROS) production, cardiac SIRT3 and Mn SOD levels were measured and analyzed. RESULTS: Compared with those in WT mice, cardiac SIRT3, Mn SOD and catalase expression decreased in SIRT3 KO mice. Arrhythmia was detected in SIRT3 KO mice under sham treatment. I/R triggered serious arrhythmia in WT mice and aggravated arrhythmia in SIRT3 KO mice (P<0.05). SIRT3 KO mice showed increased ROS production after I/R compared with WTI/R mice (P<0.05). NAD treatment significantly increased cardiac SIRT3 and MnSOD activity, inhibited ROS production and consequently suppressed I/R-induced arrhythmia in WT mice. However, NAD+ induced cardioprotctive effects were blunted in SIRT3 KO mice. CONCLUSION: Impairment of SIRT3 expression with subsequent ROS production plays an important role during I/R-induced arrhythmia and protection of SIRT3 activity may help prevent I/R-induced arrhythmia.