MMP9 and atrial fibrillation: In addition, we observed that Ang-II infusion significantly increased atrial fibrosis in SD rats with positive Masson staining, increased MMP-9, collagen Iα and collagen III α expression (Figures 4C–M), and increased susceptibility to AF, including promoted the number of AF episodes and extended AF duration, shortened AERP and prolonged AERPd (Figures 4N–R), and cardiac color Doppler ultrasound confirmed left atrial dysfunction (LADS), including enlarged LAESVI and decreased LAEF and LAFI (Figures 4S–U) compared with saline injected SD rats.