We report the findings of a patient with post-cardiac transplant mediastinitis detected by 67Ga-citrate imaging. Fever and leukocytosis were the first clinical signs suggesting infection. The usual diagnostic modalities, including CT and ultrasound, failed to identify the site of infection. A 67Ga scan showed intense abnormal uptake behind the sternum. The site of uptake was shown by necropsy to be necrotic tissue involving cardiac sutures, pulmonary arteries, and the aorta due to infection with Haemophilus aphrophilus.