Heartworms were clearly visualized on the echocardiogram as echogenic, spot-like or infrequently linear patterns within echofree cardiac cavities and pulmonary arteries. The mechanical sectoscanner appeared superior to the electronic linear array scanner in detecting heartworms harbored in the pulmonary trunk and a part of the right pulmonary artery. Both scanners, however, were valuable diagnostic means for visualizing heartworms in the right atrium, ventricle, and ventricular outflow tract, and the venae cavae.