Ventricular dysfunction and high hypertrophy may influence surgical outcome in aortic stenosis. Our aim was to determine whether an excessive left ventricular mass index (LVMI) discriminates different risk profiles in aortic stenosis with low ventricular ejection fraction (LVEF). Three hundred and thirty-nine patients with severe aortic stenosis underwent valve replacement (Mar-1994 and Nov-2001). LVMI values over the superior quartile were considered increased. Mortality models were constructed in global and LVEF<or=50% groups. In-hospital mortality was higher in increased LVMI group: 9.6 vs. 1.9%, P<0.01. In LVEF<or=50%-increased LVMI patients this mortality was also higher: 26.3 vs. 2.4%, P<0.05. Patients without LV dysfunction and increased LVMI did not show significant difference: 4.7 vs. 1.8%, P=0.41. Chronic renal failure (OR: 11.72, P<0.05), cardiopulmonary bypass time (OR: 1.03, P<0.01) and LVMI (g/m(2)) (OR: 1.01, P<0.01) were associated with mortality. In patients with LVEF<or=50%, LVMI was the strongest predictor of death. Cummulative mortality was higher with increasing LVMI and low LVEF. In conclusion, LVMI in patients with severe aortic stenosis and low LVEF might discern two different situations: an advanced cardiomyopathy with excessive hypertrophy (high LVMI-low LVEF) with poor prognosis, and an inadequate adaptive hypertrophy (low LVMI-low LVEF) in patients with afterload mismatch and more favorable outcome.