Introduction: Echocardiography plays an important role in the diagnosis of heart disease. However, sometimes misdiagnosis information is also provided. Methods and Results: We report a rare case of preoperative echocardiography misdiagnosed as a primary mitral valvular tumor with severe regurgitation. During the surgery procedure, the true lesion was found to be mitral valve leaflet prolapse due to degenerative mitral valve disease. Conclusions: For individual patient, it may need to combine clinical symptoms and wide use of echocardiography and CT or MRI to make the optimal clinical decision.