Small extracellular vesicles (sEVs) are nanometer-sized membranous vesicles that contribute to the pathogenesis of atrial fibrillation (AF). Here, we investigated the role of sEVs derived from patients with persistent AF in the pathophysiology of AF. First, we evaluated the pathological effects of sEVs derived from the peripheral blood of patients with persistent AF (AF-sEVs). AF-sEVs treatment reduced cell viability, caused abnormal Ca2+ handling, induced reactive oxygen species (ROS) production and led to increased CaMKII activation of non-paced and paced atrial cardiomyocytes. Next, we analyzed the miRNA profile of AF-sEVs to investigate which components of AF-sEVs promote arrhythmias, and we selected six miRNAs that correlated with CaMKII activation. qRT-PCR experiment identified that miR-30a-5p was significantly down-regulated in AF-sEVs, paced cardiomyocytes, and atrial tissues of patients with persistent AF. CaMKII was predicted by bioinformatics analysis as a miR-30a-5p target gene and validated by a dual luciferase reporter; hence, we evaluated the effects of miR-30a-5p on paced cardiomyocytes and validated miR-30a-5p as a pro-arrhythmic signature of AF-sEVs. Consequently, AF-sEVs-loaded with miR-30a-5p attenuated pacing-induced Ca2+-handling abnormalities, whereas AF-sEVs-loaded with anti-miR-30a-5p reversed the change in paced cardiomyocytes. Taken together, the regulation of CaMKII by miR-30a-5p revealed that miR-30a-5p is a major mediator for AF-sEVs-mediated AF pathogenesis. Accordingly, these findings suggest that sEVs derived from patients with persistent AF exacerbate arrhythmogenesis via miR-30a-5p.