We reported a 51-yr-old female with radiation-induced chronic constrictive pericarditis. At age 29, she had received a mastectomy and postoperative irradiation because of left breast cancer. At age 45, she had syncope and was diagnosed with complete atrioventricular block and a pacemaker was implanted. At that time, pericardial thickening with effusion was noted. The following year, tricuspid regurgitation was noted. On catheter study, a dip and plateau pattern of the right ventricular pressure curve appeared. At age 50, tricuspid regurgitation worsened due to the lead wire of the pacemaker compressing the leaflet, and the pacemaker was reimplanted. However, the following year, she complained of general fatigue and dyspnea and was admitted to our hospital. On 67Ga study, diffuse accumulation in the cardiac region appeared. There was no perfusion defect detected in the left myocardium, but right myocardial damage was suspected by thallium study. In 99mTc-HSA RI angiography, right atrium dilatation appeared and a pericardial halo around the ventricles was seen. She underwent pericardectomy, tricuspid replacement and pacemaker reimplanted, but she died. On autopsy, pericardial thickening and adhesion, right myocardial fibrosis, the fibrotic change of the bundle branches were seen. We reported a case of radiation-induced constrictive pericarditis. Radionuclide studies were useful in diagnosing and following the patient.