Doppler echocardiographic contribution of atrial systole to left ventricular filling (AC) was studied in 20 patients with mitral stenosis and compared with that obtained from 15 matched controls in a prospective study. AC in mitral stenosis as a percentage of total filling volume was 8 +/- 2.8% compared to 12.5 +/- 3.3% in control subjects (p < 0.001) and was weakly correlated to diastolic filling period (r = -0.45), mitral valve orifice resistance (r = -0.36) and heart rate (r = 0.36). An increase in mitral valve orifice area following balloon mitral valvuloplasty (0.78 +/- 0.12 to 1.72 +/- 0.4 cm2, p < 0.0001) resulted in an increase in AC to near normal values (8 +/- 2.8% to 12.5 +/- 3.8%, p < 0.001) coupled with an increase in cardiac index and a significant decrease in diastolic filling period and left atrial size. In conclusion, AC in young patients with severe mitral stenosis is decreased proportionately less than that reported in the older patients, is weakly correlated to mitral orifice resistance and normalises following a successful mitral valvuloplasty.