Atrial fibrillation (AF) is a common tachyarrhythmia and may cause serious complications, such as stroke. When atrial pressure was elevated, the effect refraction period (ERP) was shortened and the conductivity in atria was slowed and the heterogeneity of different parts of atria was increased. These changes facilitate the occurrence and maintenance of AF. Recent researches demonstrated that pulmonary veins (PVs) are important sources of ectopic beats in the initiation of paroxysmal AF. In patients with drug-resistant chronic AF and structural heart disease, after electrical cardioversion, the PVs are also the dominant trigger in reinitiating AF.1 Yamane et al2 reported that, AF patients were often with dilated PVs if the AF was initiated by focal activity in PVs. Atrial myocardial fibers wrap around the PVs entering the left atrium to form PV myocardial sleeves (PVMSs), and this structure is the origin of focal activity. Little is known about the effects of elevated atrial pressure on PV electrophysiology. In the present study, we found that, spontaneous activity in PVMSs could be induced by elevated atrial pressure and it could affect the atrial rhythm.