“…Of dogs with cardiac HSA (cHSA), between 83 and 100% have been found to have pericardial effusion. 1,9,10 In a study of 9 dogs with cHSA undergoing necropsy, invasion into and rupture of right atrium was noted in 2 dogs. 9 Given the aggressive nature of this type of tumor, the extension beyond the right atrium and tricuspid valve into the right outflow tract is remarkable.…”