We performed transapical transcatheter aortic valve implantation on an 87-year-old woman with severe aortic valve stenosis. Because of the narrow left ventricular outflow tract, annular positioning of the prosthetic valve proved challenging. During positioning, the prosthetic valve was accidentally dislodged from the balloon catheter and dropped into the left ventricle. Attempted catheter retrieval was unsuccessful. We therefore converted to open surgery without delay. After aortotomy, to our surprise, the prosthesis could not be found, neither in the left ventricle nor in the ascending aorta. Transesophageal echocardiography failed to reveal the location of the missing prosthesis. Fluoroscopy finally displayed the prosthesis in the descending aorta at the level of the left atrium. We proceeded with aortic and mitral valve replacement and closed the sternum. Under fluoroscopic guidance, the prosthetic valve was secured to the wall of the abdominal aorta in an infrarenal position by dilatation with a balloon catheter. This case shows that we should be alert to septum hypertrophy or a narrow left ventricular outflow tract during transapical aortic valve implantation. In such anatomical situations, we recommend advancing the sheath of the application system directly below the annular plane and positioning the prosthesis from this point.