Replacement of the aortic valve exposes the left ventricle to myocardial ischaemia and imposes on it abrupt changes in loading conditions and geometry. We studied the immediate changes in the left ventricular function of patients undergoing aortic valve replacement by transoesophageal echocardiography. Patients with aortic regurgitation responded to surgery with a decrease in global systolic function associated with a fall in preload. Patients with aortic stenosis showed an impairment in myocardial contractility and ventricular filling, and their global systolic function did not improve despite the marked reduction in afterload. This can be a consequence of inadequate myocardial protection and intra-operative ischaemic injury of the hypertrophic myocardium. Information provided by transoesophageal echocardiography contributes to optimal and individualized management of the period immediately after aortic valve replacement.