BACKGROUND--Gender differences in cardiac size have been described in normal humans and animals and in response to pressure overload. To examine the influence of gender on the left ventricular response to pressure overload, clinical, haemodynamic, and echocardiographic data were analysed in the 232 adults with isolated aortic stenosis enrolled in the Balloon Valvuloplasty Registry. METHODS AND RESULTS--There were 92 men (mean (SD) age 75 (11) years) and 140 women (79 (9) years; P = 0.002). Women had similar symptoms (New York Heart Association class) but lower overall functional status than men (P = 0.008). Catheterisation data showed similar valve area indices (mean (SD) (0.30 (0.09) in men and 0.31 (0.13) cm/m2 in women) but higher peak and mean gradients in women (peak 74 (30) v 63 (22) mm Hg; mean 61 (21) v 54 (18) mm Hg; both P < or = 0.01). On M mode echocardiography women had greater septal and posterior wall thickness but similar cavity diameter, after normalising dimensions to body surface area, resulting in higher relative wall thickness (0.60 (0.20) v 0.50 (0.15); P = 0.0002). Left ventricular mass index was similar in women and men (166 (59) v 159 (50) gm/m2 respectively), however, the prevalence of left ventricular hypertrophy according to sex specific criteria was 54% in men and 81% in women (P = 0.0001). Multiple logistic regression models that adjusted for age, functional status, fractional shortening, and left ventricular systolic pressure found the presence or absence of hypertrophy to be independently associated with gender (P < or = 0.002). Left ventricular systolic function tended to be better in women, who had a higher cardiac index (2.5 (0.8) v 2.3 (0.6) 1/min/m2; P = 0.01), left ventricular peak systolic pressure (211 (36) v 192 (35) mm Hg; P = 0.0001), and echo fractional shortening (32 (13) v 28 (12)%; P = 0.05); however, these differences were reduced when patients with regional wall motion abnormalities were excluded. CONCLUSIONS--In this population of elderly patients undergoing balloon dilatation of isolated aortic stenosis, left ventricular chamber geometry was different in men and women. Because this was a selected population, gender should be further evaluated as a possible determinant of the cardiac adaptation to chronic pressure overload.