A patient underwent aortic valve closure for de novo aortic insufficiency that had deteriorated to severe insufficiency during six months of support with a continuous flow left ventricular assist device (cf-LVAD). Aortic insufficiency was initially noted one month after LVAD implantation, and then deterioration quickly developed. Right heart catheterization revealed that when the rotational speed of the cf-LVAD was increased, the cardiac index was decreased by an increase in regurgitant volume, as shown by echocardiography. During surgery, fusion and shortening of the aortic leaflets as well as left coronary ostial occlusion were observed. Direct aortic closure improved hemodynamics. Thrombus formation on the aortic valve shown by echocardiography in the early postoperative period may be a trigger of aortic insufficiency. Control of the cf-LVAD rotational speed is likely required to prevent aortic insufficiency.