A 13-month-old Guernsey heifer was admitted on emergency for vague signs of lethargy, bloat, hyporexia and a sudden onset of diarrhoea. On presentation, the heifer was tachycardic, febrile and diffusely oedematous. Bloodwork demonstrated no electrolyte abnormalities, increased liver enzymes, low total protein, increased lactate and a mild leukocytosis characterised by neutrophilia. Ultrasonographic exam revealed the presence of tricavitary effusion, a diffuse, hepatomegaly and an abnormal heart valve. Humane euthanasia was elected and a full autopsy was performed. On postmortem examination, the heart was twice the normal size and had two congenital defects, a ventricular septal defect and pulmonic valve leaflet atresia. Two valvular myxomas were present in the area of the pulmonic valve and likely contributed to further cardiac damage. Final postmortem diagnosis was congestive heart failure secondary to congenital heart defects and valvular myxomas. A postmortem serum cardiac troponin I was likely indicative of myocardial injury.