The natural history of left ventricular spontaneous contrast. Spontaneous contrast in the left ventricle is an unusual entity. We retrospectively studied 16 patients who were found to have spontaneous contrast present on two-dimensional echocardiograms, specifically noting their clinical characteristics, the reproducibility of this phenomenon, the presence of thrombi and embolic events, and prognostic implications. Diagnoses included ischemic heart disease in nine patients, dilated cardiomyopathy in six patients, and hypertensive cardiomyopathy in one patient. The mean ejection fraction was 17.6%. There were six thromboembolic events in four patients. The spontaneous contrast was reproducible for periods of time up to 39 months. Patients who had improvement in their left ventricular dysfunction or who underwent aneurysmectomy had disappearance of the spontaneous contrast. Those patients who had spontaneous contrast reproduced on subsequent echocardiograms did not seem to have a worse prognosis than patients with similarly depressed ventricular function, but a larger study is necessary to verify this. 