Abstract: A 65-year-old woman with a complete atrioventricular block was diagnosed as having cardiac sarcoidosis. 18F-FDG PET/CT imaging without unfractionated heparin loading revealed systemic abnormal uptake indicating sarcoidosis. However, the cardiac lesions were vague because of the physiological FDG uptake. One month later, 18F-FDG PET/CT using heparin loading was performed to evaluate the lesion activity prior to the start of steroid administration. 18F-FDG PET/CT imaging with heparin loading showed the cardiac lesions more clearly and suppressed the FDG uptake in normal myocardium. Heparin loading during FDG PET/CT may be useful for detecting cardiac involvement in patients with cardiac sarcoidosis.