Eustachian valve endocarditis is a rare cause of infective endocarditis. We present the case of a 72-year-old woman in whom this was found after a lengthy search. We then go on to discuss the prevalence and some of the difficulties found in the investigation of this disease.<Learning objective: The Eustachian valve (EV) is a valve at the junction of the inferior vena cava and right atrium that in fetal life ensures oxygen-rich blood flows through the foramen ovale into the left side of the heart. In adult life it is vestigial, though it can be prominent and can be a site for vegetations. EV endocarditis can be easily missed if not searched for – if the clinical picture appears to be one of endocarditis, one must remember this valve.