Background: Hyperhomocysteinemia (HHcy) is one of the major risk factors of cardiovascular diseases. Metformin acts as a cardioprotective role in several cardiovascular diseases, including ischemia/ reperfusion, atherosclerosis, and myocardial infarction. However, whether metformin protects against HHcy-induced cardiac hypertrophy is unclear. Methods and Results: HHcy model was established in C57BL/6 mice with high L-methionine (L-MET) diet for 12 weeks. AC16 cells were exposed to homocysteine (Hcy) and then intervened with different concentrations of metformin in in vitro studies. The results showed that HHcy was able to induce cardiac hypertrophy, and metformin could abrogate this effect. HHcy increased the fibrosis area and induced apoptosis in the myocardium, whereas metformin could reverse the detrimental effects above. TUNEL assay showed that metformin was able to decrease Hcy-induced apoptosis in AC16 cells. Moreover, western blotting assay revealed that metformin could decrease Hcy-induced expression of Bax and cleaved caspase3, and increase the expression of Bcl-2. Conclusions: This study demonstrates that metformin is able to attenuate HHcy-induced cardiac hypertrophy by decreasing myocardial fibrosis and apoptosis. (c) 2020 Published by Elsevier Masson SAS.