Using transesophageal echocardiography (TEE), intraatrial thrombus was visualized clearly with fine mistlike echoes which are reported to be detected when the blood flow is stagnant or ceased. The echoes showed slow, clockwise, circular movement in the left atrium, and were confirmed to show the real flow with two-dimensional color Doppler TEE. They were different from those echoes seen as contrast echoes which are more coarse, more echogenic, and accompanied with slight side lobes.

TEE demonstrated slight mitral regurgitation which was not detected with conventional echocardiography conducted preoperatively. It is not certain whether such slight regurgitation has some clinical significance or not. However, accompanied with drainage flow from the pulmonary veins, the trivial regurgitation seemed to cause slow circulatory movement in the left atrium and turbulant flow around the left auricle. As we previously reported, the blood in the left atrium is strongly stirred in the cases or marked mitral regurgitation. This might explain the reason why the intraatrial thrombus is rarer in the case of mitral regurgitation than in pure mitral stenosis.