BACKGROUND: Spontaneous echo contrast(SEC) is known to predict the increased incidence of thromboembolism in a variety of heart diseases. Transesophageal echocardiography can be useful for the detection of SEC due to proximity of the probe to the left atrium. We performed this study (1) to evaluate the incidence of SEC in mitral stenosis and its relation to the past history of thromboembolism and (2) to characterize the echocardiographic and hemodynamic indices in patients with SEC compared with those without SEC. METHODS: Transesophageal and thransthoracic echocardiographies were done in 89 patients with mitral stenosis. Biplane probe was used in transesophageal echocardiography. In 47patients cardiac catheterization and angiography were performed. RESULTS: (1) SEC was found in 56 out of 89 patients(63%), and left atrial thrombus was found in 32 patients. (2) Left atrial dimension was larger in patients with SEC than in patients without SEC(57.3%+/-8.4mm vs 49.3+/-6.8mm, p<0.05) and mitrial valve area was smaller in patients with SEC than in patients without SEC(0.85+/-0.27cm2 vs 0.97+/-0.24cm2) (3) Association of SEC to thrombi or previous history of arterial embolism showed a high sensitivity and negative predictive value. CONCLUSION: SEC was an useful finding to predict the increased risk of thromboembolism in patients with mitral stenosis. Patients with SEC had severe mitral stenosis than patients without SEC.