A case of atypical movement of the intimal flap (tear) during aortic aneurysm dissection is reported. Aortic dissection is caused by the sudden development of a tear in the aortic intima, opening the way for a column of blood driven by the force of the arterial pressure to enter the aortic wall, destroying the media and stripping the intima from the adventitia for variable distance along the length of the aorta. Echocardiographically, aortic dissection is characterized by separation of the normal single dominant echo from the aortic wall in the region of the dissection into two discrete echoes. The inner echo arises from the tunica intima, whereas the outer echo arises from the medial and adventitial structures external to the tear and it is possible to identify two lumens separated by an intimal flap within the aorta. The two echoes generally move in unison with one another, i.e. movement of the flap away from the true lumen during systole and recoil during diastole as the blood flows from true to false lumen. The dissection flap can also move inward during systole owing to the suction caused by high-velocity flow (Venturi effect), as shown in this case report. In any instances, motion of the intimal flap during the cardiac cycle is strong evidence of dissecting aneurysm.