BACKGROUND: It has been reported that mechanical damage occurs when regurgitant flow from aortic regurgitation (AR) directly impinges on the anterior mitral valve leaflet (AML). However, only a few cases of mitral valve perforation have been reported. Previous reports suggest that AR in such cases tends to be Grade 3 or higher and that haemodynamic damage to the mitral valve due to AR may be proportional to its severity. On the contrary, no cases of mitral valve perforation due to mild AR have been reported. CASE SUMMARY: In 2011, a 56-year-old man presented with mild AR towards the AML, revealed on a transthoracic echocardiogram. In 2016, 3 months before admission, the patient had been experiencing intermittent fevers of over 40°C, which did not improve, and was referred to our hospital. A detailed examination revealed a vegetation on the AML where the aortic valve was displaced, and the site was perforated. The AR was mild to moderate. Blood cultures were positive for DISCUSSION: This case indicates that even mild AR directed at the AML can damage the AML, raising IE risk. Consequently, mild AR deviation towards the AML should be considered a potential risk factor for AML IE.