The echocardiographic findings were studied in 25 patients with pathologically proved left atrial myxoma. All patients had M-mode echocardiograms and 14 had two-dimensional studies. Seventeen patients had pre- and postoperative echocardiograms. Clinical, hemodynamic, angiographic and pathologic correlations were made. The diagnosis of left atrial myxoma was suspected clinically in only three patients before the echocardiographic study. The correct echocardiographic diagnosis was made in 24 patients; in one patient it was missed with an M-mode study. In addition to the usual "mass" of extraneous echoes seen behind the mitral valve in the left atrium, the only other consistent abnormality on M-mode study was a decreased EF slope of the mitral valve (3.9 +/- 3.5 cm/s). The following dimensions were usually normal: left atrium, 4.0 +/- 0.7 cm; right ventricle, 2 +/- 0.7 cm; left ventricular end-diastolic diameter, 4.8 +/- 0.6 cm and end-systolic diameter, 2.9 +/- 0.5 cm. The mean percent of shortening was 37 +/- 5%. Two-dimensional echocardiography correctly identified the presence of a left atrial myxoma in all 14 patients studied. It provided additional information regarding size, shape, mobility, surface characteristics and site of insertion of the tumor. Eighteen patients had hemodynamic and angiographic studies. Coronary artery disease was found in one patient with typical angina. Echocardiography is an excellent technique for visualizing atrial myxoma. Cardiac catheterization is probably not needed before excision of a myxoma.