Both the clinical and diagnostic signs, as well as the differential diagnoses, associated with cardiac tamponade are discussed. The case study will focus on Casey, a 9 year old female spayed Labrador, who presented to Cornell's Cardiology Service with significant evidence of pericardial effusion. As one of the few underlying causes for pericardial effusion, cardiac tumors will be discussed as they relate to Casey. In particular, cardiac hemangiosarcoma (HSA) as it relates to the case at hand will be discussed, along with treatment options and prognosis.