Mediastinal radiotherapy (XRT), which is frequently used to treat thoracic malignancies and lymphomas, is associated with significantly improved survival for cancer patients. However, in many instances, there is unavoidable irradiation of healthy surrounding tissues, which can cause long-term side effects. Among the myriad potential side effects, radiation-associated cardiac disease (RACD) can develop gradually over several years following XRT. While newer XRT-delivery techniques have reduced doses and cardiac involvement, a major current issue remains the development of RACD in patients exposed to XRT decades ago. As a result, appropriate recognition of RACD is warranted in day-to-day clinical practice. RACD is a spectrum of deleterious effects ranging from pre-clinical findings to symptomatic clinical disease and includes myocardial fibrosis/dysfunction; valvular heart disease (regurgitation and/or stenosis); vasculopathy, including coronary artery disease; pericardial disease; and conduction abnormalities.