Abstract: OBJECTIVE To investigate the effects of telmisartan on the expression of potassium channel and Connexin 40(Cx40) in atrial myocytes of patients with atrial fibrillation(AF). METHODS Eleven patients with AF were selected as the study subjects, cardiopulmonary bypass was established during cardiac surgery and the right atrial appendage tissues were excised. Acute enzymatic isolation was used to obtain single atrial myocytes, atrial myocytes were divided into four groups:control group(untreated), low dose group(10 μmol·L^-1 telmisartan), medium dose group(30 μmol·L^-1 telmisartan), and high dose group(100 μmol·L^-1 telmisartan). CCK-8 method was used to detect the viability of atrial myocytes in each group; qRT-PCR was used to detect the expressions of potassium channels related genes Kir2.1, Kir3.4, Kv4.3, Kv1.5, and Cx40 mRNA; the expressions of Kir2.1, Kir3.4, Kv4.3, Kv1.5 and Cx40 proteins were detected by Western blotting. RESULTS Compared with the control group, the survival rate of atrial myocytes, Kir3.4, Kv4.3, and Kv1.5 mRNAs and proteins expression levels in different doses of telmisartan were significantly increased(P<0.05), the high dose group was significantly higher than the middle and low dose groups(P<0.05); the expression levels of Kir2.1 and Cx40 mRNAs and proteins in atrial myocytes were significantly decreased(P<0.05), the high dose group was significantly lower than the middle and low dose groups(P<0.05). CONCLUSION Telmisartan may antagonize atrial remodeling in AF patients by affecting the expression of potassium channel-related genes and down-regulating the expression of Cx40 in atrial myocytes.