To assess the passive and the active phases of left atrial (LA) emptying, LA volumes and function were studied in 15 patients with mitral stenosis (MS) in sinus rhythm and in 11 normal subjects (NL) with two-dimensional echocardiography with simultaneous electrocardiograms. LA and left ventricular (LV) volumes were measured with the biplane area-length method. LA maximal and minimal volumes were measured at mitral valve opening and closure, respectively. In addition, LA volume was measured at onset of atrial systole (beginning of the P wave on the electrocardiogram). LA volumes were larger in MS compared with NL; Maximal 122 +/- 65 cm3 versus 46 +/- 12 cm3, p less than 0.001; onset of atrial systole 108 +/- 63 cm3 versus 29 +/- 12 cm3, p less than 0.001; minimal 90 +/- 60 cm3 versus 18 +/- 7 cm3, p less than 0.001. LA passive emptying volume (maximal minus volume at onset of atrial systole) was not statistically different in MS compared with NL, while LA active emptying volume (volume at onset of atrial systole minus minimal) was larger in MS compared with NL (17 +/- 5 cm3 versus 11 +/- 5 cm3, p less than 0.05). The net result was normal LA total emptying volume (maximal minus minimal) MS 32 +/- 11 cm3, NL 28 +/- 5 cm3. In contrast, the LA emptying fractions were significantly decreased in MS compared with NL (passive 0.13 +/- 0.08 versus 0.39 +/- 0.1, p less than 0.0001, active 0.19 +/- 0.08 versus 0.38 +/- 0.07, p less than 0.0001, total 0.30 +/- 0.1 versus 0.62 +/- 0.07, p less than 0.0001).(ABSTRACT TRUNCATED AT 250 WORDS)