To test the feasibility of imaging the left main coronary artery (LMCA) noninvasively as a means of detecting left main coronary artery disease, we studied 73 patients who underwent cardiac catheterization and cross-sectional echocardiography. Fifty-two had a normal LMCA (controls) and 21 had significant obstruction (greater than or equal to 50% luminal reduction). The apical, tomographic, cross-sectional, phased-array, echocardiographic approach was used, and the LMCA was imaged in 52 of 73 patients (71%). In 34 of 36 controls (94%) the LMCA was correctly judged as having no luminal obstruction. In the other two, and asymmetric, high-intensity echo in one wall of the artery suggested atherosclerotic disease, but coronary angiography revealed no obstruction. In 12 of 16 patients (75%) in whom significant LMCA disease was imaged, obstruction was predicted by echocardiographic criteria of either luminal irregularity or an asymmetric, high-intensity echo in the arterial wall. This preliminary study suggests that cross-sectional echocardiography appears to be a feasible, noninvasive technique to image the LMCA and to detect hemodynamically significant luminal obstruction.