Aim By establishing methamphetamine (METH) poisoning model and myocardial cell poisoning model in SD rats, to detect the expressions of gap junction protein connexin 43 (Cx43) and its phosphorylation (p-Cx43) at S368 site. By examining the expressions of Cx43 and its S368 site p-Cx43 in human myocardial tissues after taking METH, to analyze the relationship between the expressions of Cx43, p-Cx43 and METH-induced myocardial toxicity, and to investigate the role of Cx43 and its S368 site p-Cx43 in myocardial toxicity induced by METH. Methods METH chronic poisoning animal model in SD rats and primary METH poisoning cell model of cardiac muscle in neonatal SD rats were established. The proteins were extracted and the expressions of Cx43 and p-Cx43 proteins were detected by Western blot. The relationship between the levels of Cx43 and its S368 site p-Cx43 and METH-induced myocardial toxicity was analyzed. The myocardial tissues of METH users confirmed by toxicity test in Forensic Judicial Appraisal Center of Guizhou Medical University were collected as experimental group and those without any drugs as control group. After routine paraffin section, HE staining was used to observe the structural changes of myocardium in two groups. Immunohistochemical staining and Western blot were used to detect the expressions of Cx43 and its S368 site p-Cx43. Results (1)Expressions of Cx43 and its S368 site p-Cx43 in METH chronic poisoning animal model was significantly lower than those in control group (P＜0.05). (2)Expressions of Cx43 and its S368 site p-Cx43 in METH poisoning cell concentration and time gradient model were significantly lower than those in control group (P＜0.05). (3)Compared with the control group, the atrophy, necrosis and focal hemorrhage of human cardiac myocytes were observed in the experimental group. (4)Compared with the control group, the expression levels of Cx43 and S368 site p-Cx43 in human myocardium in the experimental group were lower than those in the control group, mainly expressed as the decrease of brown-yellow staining at intercalated disc between cardiac myocytes, and some of them showed lateral membrane changes. (5)Expressions of Cx43 and S368 site p-Cx43 proteins of human myocardium in experimental group were lower than those in control group (P＜0.05). Conclusion METH can reduce the expressions of Cx43 and its S368 site p-Cx43 in myocardium, thus destroying the structure of myocardium and affecting the normal function of heart.