AimTo observe the change of the distribution and expression levels of connexin 40 (Cx40) in right atrial myocardium of people with no-atrial fibrillation (no-AF) and patients with different types of atrial fibrillation (AF), and to study the associations among distribution and expression changes of Cx40 with AF subtypes, right atrium (RA) size and initiation and development of AF.MethodsThe total 23 samples of right auricular appendage were collected.Five were designed to no-AF group, six patients with paroxysmal AF (PX), five patients with persistent AF (PS) and seven patients with permanent AF (PM) served as AF groups.RA size by echocardiographic analysis was indexed to body surface area.Expression and distribution of Cx40 were examined by immunoconfocal microscopy.The mRNA content of Cx40 was measured by relatively real-time quantitative polymerase chain reaction (real-time PCR).And protein expression level of Cx40 was studied by Western blotting.ResultsRA size of different AF subgroups was higher than that in no-AF group (p<0.05 or p<0.01).Immunoconfocal microscopy showed that Cx40 was mainly localized to the intercalated disc of cardiomyocytes in no-AF group, whereas exhibited heterogenous distribution in AF groups.The mRNA and protein expression levels of Cx40 were increased in PX group compared with no-AF group, however, Cx40 reduced in PS group and even lower in PM group (p<0.05 or p<0.01).The protein expression of Cx40 correlated negatively with