Previously, we found that the miR-217 expression level was increased in hearts from chronic heart failure (CHF) patients by using miRNA profile analysis. This study aimed to explore the role of miR-217 in cardiac dysfunction. Heart tissue samples from CHF patients were used to detect miR-217 expression levels. A type 9 recombinant adeno-associated virus (rAAV9) was employed to manipulate miR-217 expression in mice with thoracic aortic constriction (TAC)-induced cardiac dysfunction. Cardiac structure and function were measured by echocardiography and invasive pressure-volume analysis. The expression levels of miR-217 were increased in hearts from both CHF patients and TAC mice. Overexpression of miR-217 in vivo aggravated pressure overload-induced cardiac hypertrophy, fibrosis, and cardiac dysfunction, whereas miR217-TUD-mediated downregulation of miR-217 reversed these effects. PTEN was predicted and validated as a direct target of miR-217, and re-expression of PTEN attenuated miR-217-mediated cardiac hypertrophy and cardiac dysfunction. Importantly, cardiomyocyte-derived miR-217-containing exosomes enhanced proliferation of fibroblasts in vitro. All of these findings show that miR-217 participates in cardiac hypertrophy and cardiac fibrosis processes through regulating PTEN, which suggests a promising therapeutic target for CHF.