Today, mitral valve replacement is performed under cardioplegic arrest with cross-clamping of the ascending aorta. In the case reported here, mitral valve replacement was performed with an on-pump beating heart technique without cross-clamping the aorta because of diffuse adhesion around the tube graft. A 36-year-old man had undergone a Bentall operation (aortic root replacement + coronary reimplantation) via median sternotomy because of type I aortic dissection 4 years previously in our cardiac center. He was admitted to the hospital complaining of palpitation and dyspnea on mild exertion. Transthoracic echocardiography study revealed third-degree mitral insufficiency. Mitral valve replacement was carried out through re-median sternotomy with an on-pump beating heart technique without crossclamping the aorta. On-pump beating heart mitral valve replacement without a cross-clamp offers a safe approach when excessive dissection is required to place a crossclamp on the ascending aorta.