An adult Jack Russel terrier dog presented for evaluation of large-volume peritoneal and pleural effusion. Echocardiography revealed scant pericardial effusion and abnormally thickened pericardium. Electrocardiography revealed complete atrioventricular block with junctional and ventricular escape beats and occasional ventricular premature complexes. Computed tomography of the thorax confirmed diffuse abnormal thickening of the pericardium, and a tentative diagnosis of constrictive-effusive pericarditis was made. The dog underwent subtotal pericardiectomy to remove the parietal pericardium and permanent epicardial pacemaker implantation to manage bradycardia. Based on pericardial histopathology and immunohistochemistry, a diagnosis of pericardial hemangiosarcoma was made. Systemic chemotherapy was initiated with doxorubicin 1 month after surgery. Despite initial improvement with chemotherapy, the dog was euthanized 4 months after surgery because of development of recurrent pleural effusion. To the author's knowledge, this is the first case report in dogs to describe isolated pericardial location of hemangiosarcoma resulting in constrictive-effusive pericarditis.