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MicroRNAs (miRNAs) play a role in cardiac remodelling. MiR208a is essential for the expression of the genes involved in cardiac hypertrophy and fibrosis. The mechanism of regulation of miR208a involved in cardiac hypertrophy by mechanical stress is still unclear. We sought to investigate the mechanism of regulation of miR208a and the target gene of miR208a in cardiac cells by mechanical stretch.Rat H9c2 cells (cardiac myoblasts) grown on a flexible membrane base were stretched via vacuum to 20% of maximum elongation at 60 cycles/min. Mechanical stretch significantly enhanced miR208a expression after 4 h of stretch. Exogenous addition of transforming growth factor-β1 (TGF-β1) increased miR208a expression, and pre-treatment with TGF-β1 antibody attenuated the miR208a expression induced by stretch. Mechanical stretch significantly increased endoglin and collagen I expression for 6–24 h. Exogenous addition of TGF-β1 and overexpression of miR208a up-regulated endoglin and collagen I expression, while antagomir208a and Smad3/4 inhibitor attenuated endoglin and collagen I expression induced by stretch. Mechanical stretch and TGF-β1 increased Smad3/4–DNA binding activity and miR208a promoter activity, and TGF-β1 antibody and Smad3/4 inhibitor decreased the Smad3/4–DNA binding activity and miR208a promoter activity induced by stretch.Cyclic mechanical stretch enhances miR208a expression in cultured rat cardiac myoblasts. The stretch-induced miR208a is mediated by TGF-β1. Mir208a activates endoglin expression and may result in cardiac fibrosis.