We studied 37 consecutive patients with mitral stenosis in sinus rhythm using transthoracic and transesophageal echocardiography to relate the presence of spontaneous echo contrast (SEC) in the left atrium with mitral valve area and left atrial dimensions. We also compared the value of left atrial area by planimetry with that of left atrial dimension by M mode in predicting presence of SEC and monitored the effect of anticoagulation on SEC. Transesophageal echocardiography demonstrated spontaneous echo contrast in 9/37 (24%) patients and thrombus in none. SEC continued to be present despite anticoagulation. Mitral valve orifice area by pressure half time method (P=0.001) and by planimetry (P=0.01), and left atrial area by planimetry (P<0.05) were predictors to presence of SEC. Left atrial dimension by M mode examination failed to predict SEC. Cut off values were mitral valve orifice </=1.4 cm(2) (agreement 86%) and left atrial area >/=25 cm(2) (agreement 81%). On multivariate analysis mitral valve area was the only independent predictor. SEC persisted despite anticoagulation. This supports the view that more than one mechanism is involved in the development of SEC.