Aortic dissection is one cause of acute aortic regurgitation, and transthoracic echocardiography and computed tomography are useful for diagnosis. We report a case of intraoperatively discovered acute aortic regurgitation caused by aortic dissection limited to the sinus of Valsalva. The patient was a 71-year-old man who regularly visited his local doctor for hypertension and diabetes mellitus. He visited the doctor with a week-long history of cough and dyspnea, and was referred to our hospital due to acute congestive heart failure. We diagnosed severe acute aortic regurgitation as the cause of the heart failure, but the aortic root dissection was not detected by transthoracic echocardiography or plain computed tomography. Since his heart failure progressively worsened even with intensive medical therapy, urgent surgery was decided on the 6th day after hospitalization. Intraoperatively, we noted that the aortic dissection was limited to the sinus of Valsalva, and had induced aortic regurgitation due to dissected and separated aortic commissure. We changed the surgical procedure from aortic valve replacement to the Bentall procedure (Piehler method). Postoperatively, the patient was intubated for 7 days and stayed in the ICU for 14 days due to treatment for pneumothorax and organizing pneumonia. He was successfully transferred to a rehabilitation hospital on the 35th postoperative day. Acute aortic regurgitation caused by aortic dissection limited to the sinus of Valsalva is rare, so we report the case based on literature reviews and as a heart team.