There is disagreement regarding the indications of surgery for cases of severe aortic stenosis (AS) with a decrease in left ventricular ejection fraction (EF) and a low aortic pressure gradient (PG), since there is a high perioperative risk associated with this condition. Hence, we investigated the surgical outcome of AS cases with impaired left ventricular function. Our department performed 144 aortic valve replacements (AVRs) for cases of AS and AS-dominant mild regurgitation (ASr) between January 2000 and September 2005. Among these cases, 9 patients had an EF under 35%, and these patients were selected as subjects and compared with a control group with an EF of more than 35%. Patients with accompanying coronary artery diseases that required treatment were excluded to avoid confounding effects on cardiac function. The mean age of the 9 subjects (4 men and 5 women) was 67.8±10.8 years old, with a range from 53 to 80 years old, and the subjects had the following mean background data: EF, 34.4±0.5%; left ventricular end-diastolic dimension (LVDd), 57.3±5.8mm; left ventricular end-systolic dimension (LVDs), 49.3±5.7mm; interventricular septum thickness (IVSth), 11.9±1.9mm; and left ventricular posterior wall thickness (LVPWth), 11.1±2.6mm. Characteristics such as left ventricular dilatation and thinning of the left ventricle myocardium were noted in these data. The cases were classified as severe AS because the mean aortic valve area (AVA) was 0.58±0.2cm², but the peak aortic pressure gradient (peak PG) (65.2±32.7mmHg) in the 9 subjects was lower than that of the control group (97.0±65.2mmHg). All 9 subjects underwent aortic valve replacements (AVRs), with simultaneous mitral annuloplasty (MAP) in 3 cases, mitral valve replacement (MVR) in 1 case and performance of a Maze procedure in 1 case. No deaths occurred while the patients were in hospital. Postoperative complications included 2 cases of transient atrial fibrillation and 1 case of postoperative bleeding requiring rethoracotomy for hemostasis. The EF in the late postoperative period showed improvement in 8 cases and was unchanged in the remaining case; the mean postoperative EF was 56.9% for the 9 subjects. All cases were rated as improved based on the NYHA classification of cardiac performance, and the significant improvement in EF in 8 of the 9 cases suggests that surgery is safe and can improve prognosis for patients with advanced AS with myocardium thinning and decreased EF.