A man in his early 70s presented with heart failure syndrome. The clinical diagnosis was possible constrictive pericarditis. However, at cardiac catheterisation, there was a large step-up in oxygen saturation in the inferior vena cava between the mid-abdomen and entry into the heart. Abdominal imaging showed a large renal arterio-venous fistula, which was subsequently embolised, resulting in the resolution of the patient's symptoms.
Houghton et al. (Sun,) studied this question.