The purpose of this study was to evaluate the correlates of spontaneous echo contrast in mitral stenosis and normal sinus rhythm. Spontaneous echo contrast is associated with clot formation and embolic phenomena. It has been noted in conditions involving blood stasis, especially mitral stenosis and atrial fibrillation, but the correlates of spontaneous echo contrast in patients with mitral stenosis and normal sinus rhythm have not been extensively evaluated. The transthoracic and transesophageal echocardiograms and clinical findings of 47 patients with mitral stenosis and normal sinus rhythm were reviewed. Left atrial size, mean transmitral gradient, and valve area were measured, and the presence or absence of spontaneous echo contrast in the left atrium was noted. Spontaneous echo contrast was found in the echocardiograms of 21 (45%, group 1) of 47 patients. There was no contrast in those of the other 26 patients (group 2). Mean transmitral gradient was significantly higher in group 1 (13.6 +/- 5.2 mm Hg) than in group 2 (10.5 +/- 4.9 mm Hg) (p < 0.05). Mitral valve area was significantly smaller in group 1 than in group 2 (1.0 +/- 0.5 vs 1.4 +/- 0.5 cm2; p < 0.02). There was a trend toward a higher prevalence of significant mitral regurgitation in group 2. There was no significant difference with respect to age, left atrial size, history of embolism, or warfarin therapy. We conclude that spontaneous echo contrast in the left atrium of patients with mitral stenosis and normal sinus rhythm is common and is associated with a significantly smaller mitral valve area and higher mitral gradient.(ABSTRACT TRUNCATED AT 250 WORDS)