A total of 25 cardiac surgical trainees with no formal transesophageal echocardiography learning experience were randomly assigned by computer to a study group receiving simulation-based transesophageal echocardiography teaching via the Heartworks ( Inventive Medical , London , UK ) simulator ( n = 12 ) or a control group receiving transesophageal echocardiography teaching during elective cardiac surgery ( n = 13 ) .