Primary tumors of the left atrium are uncommon in dogs and tumor-specific diagnoses have been made only at necropsy. No reports have been found in which the diagnosis was confirmed antemortem and the tumor removed surgically. This report describes a case of obstructive paraganglioma in the left atrium of a dog and long-term survival after surgical removal of most of the tumor using cardiopulmonary bypass. Subsequently, scintigraphy demonstrated the presence of somatostatin receptors in residual tumor in the left atrium. The latter technique may be of value in establishing a definitive diagnosis in future cases of chemodectoma, extra-adrenal paraganglioma, or adrenal paraganglioma (phechromocytoma).