Objective:To investigate the relationship between the expression of myocardial connexin 43 (Cx43)in myocardial cell of the left ventricle in the cases of sudden-death due to hyperthyroid heart disease. Methods:Selected 26 autopsy cases from the Department of Forensic Medicine School of medicine,Yangtze University during 2010 to 2012. The cases were divided into two groups,13 cases in each group. ①Experimental group:9 cases male,4 female;age range is 20 to 52 with average age is 34.7 years old,Suddenly died of hyperthyroid heart disease and sudden death. ②Control group:7 males,6 females,age range is 22-60 with average age is 38.8 years old. After conventional pathological examination,Cx43 in the left ventricular muscle of each case was detected with immunohistochemic staining and image analysis. Results:In control group,the Cx43 positive staining were found in the intercalated disc. In experimental group,the Cx43 positive staining were found in the cytoplasm or side-side connection of ventricular myocyte,and the positive area of Cx43 positive particles were significantly decreased than control group (P < 0.01). Conclusion:The expression of myocardial connexin (Cx43)was significantly decreased in sudden-death patients with hyperthyroid heart disease,which suggests the decreased expression of Cx43 may have relation with sudden death of hyperthyroid heart disease.