A case of intracavitary spontaneous contrast echoes ware examined. A 76-year-old woman with acute renal failure suddenly developed precordial pain with electrocardiographic evidence of acute ischemia of the anterior myocardial wall. Two-dimensional echocardiography revealed asynergic motion of the anterior left ventricular wall. Spontaneous contrast echoes were found in the inferior vena cava and the rightside cavities. It could be described as dense granular echoes. Faint contrast echoes were found in the left ventricle. This patient exhibited ST-segment elevation in the anteroseptal leads V1-V3, but there was no increase in the serum myocardial enzyme levels. Twenty days later, two-dimensional echocardiography revealed no spontaneous contrast and an improvement of the left ventricular wall motion. The mechanism of the echogenicity in the flowing blood involves red blood cell aggregation which is greater at low flow velocity. Furthermore, it is possible that hemoconcentration promoted red blood cell aggregation in this case.