NAVLE（北美执业兽医考题）Day 770

A 11-year old male castrated Golden Retriever presents for collapse with muffled heart sounds on examination. You ultrasound the heart and obtain the following image; the right atrium (RA) and right ventricle (RV) are labeled. A large mass is seen in the right atrioventricular groove with pericardial effusion. What is the likely diagnosis?
一只11岁的雄性已绝育金毛犬由于瘫倒前来就诊，而检查时发现其心音模糊。你为其做了心脏超声得到了如下的影像，右心房和右心室已标出。在右侧房室沟处可见一很大的肿块并且伴随心包积液。最可能的诊断是什么？