Changes in left ventricular function were evaluated in twelve patients with aortic valve stenosis and in eleven patients with aortic valve regurgitation in order to find out whether the results obtained soon after aortic valve replacement persisted over a long period. All patients had been provided with a St-Jude Medical valve. Evaluation included electrocardiography, radiography of the chest, phonocarotidography and echocardiography and was performed preoperatively, then three months and five years on average in each patient after surgery. In patients with aortic valve stenosis, the left ventricular mass clearly regressed during the first three months (p less than 0.01) and continued to regress, albeit not significantly, over five years. In patients with aortic valve regurgitation, the left ventricular volume and mass regressed significantly during the first three months and remained normal for five years. No significant variation in systolic performance was observed in both groups. In spite of good overall results, 26 p. 100 of the patients had an unfavourable long-term outcome as they developed major left ventricular dilatation. Nos prosthesis dysfunction was observed, and the St Jude Medical valve caused little obstruction. Thus, with this little obstructive prosthesis the postoperative improvement obtained persisted for five years in most cases of aortic valve stenosis or regurgitation.