We present a 53-year-old woman who had shortness of breath and atypical chest pain and underwent Tc-sestamibi myocardial perfusion imaging to detect coronary artery disease. The raw data in cine format showed an incidental focus close to the heart, and SPECT/CT fused images revealed a focus of intense uptake in the left breast. The subsequent histopathologic findings and F-FDG PET/CT imaging confirmed the diagnosis as primary breast lymphoma. After 3 cycles of chemotherapy, previously visualized abnormal uptake in the left breast disappeared on the follow-up PET/CT.