PDE5 inhibition alleviated ER stress and ER stress-mediated apoptosis induced in cardiomyocytes. (A, B) Sildenafil (Sil) alleviated isoprenaline (Iso)-induced ER stress in H9c2(2–1) cells. Cells were pretreated with sildenafil for 1 h, and then exposed to isoprenaline (20 μM) for 12 h (n = 3). (C, D) Sildenafil alleviated TG-induced ER stress in cardiomyocytes. H9c2(2–1) cells were pretreated with sildenafil for 1 h, and then exposed to TG (5 μM) for 24 h (n = 3). (E, F) Flow cytometric analysis of H9c2(2–1) cells incubated with isoprenaline (20 μM) or TG (5 μM), and treated with sildenafil (10 μM) for 24 h using Annexin V-FITC and propidium iodide staining. Results shown are mean ± SEM, (n = 3). *P < 0.05 versus control. #P < 0.05 versus isoprenaline or TG.