An 11-year-old, male, Pekinese was examined because of a sporadic, nonresponsive, nonproductive cough. Radiographically there was cardiomegaly and a soft tissue mass in the cranial mediastinum. Echocardiographically, chronic degenerative valvular disease was diagnosed. Furthermore, a large anechoic structure located cranial to the right atrium was detected. Computed tomography was performed to define the mediastinal mass and a right auricle aneurysm was diagnosed. The dog died suddenly 1 day after the diagnostic imaging procedures. At necropsy, a right auricular aneurysm without discontinuity of the pericardial sac was confirmed. Intrapericardial right auricular aneurysm should be included in the differential diagnoses of cranial mediastinal masses.