Mediastinal irradiation can improve outcome for a wide range of neoplasms, including that of the lungs, breasts and oesophagus as well as lymphomas such as Hodgkin’s disease. However, when the irradiation field includes the heart, untoward late cardiac effects can develop that were underappreciated in the past. Indeed, until the mid 1960s, the heart was thought to be a relatively radioresistant organ. Even as recent as the 1980s, the issue of whether radiation exposure led to coronary artery disease was controversial and a relationship was not established until the mid to late 1990s. It was then becoming clear that the cardiovascular risks of mediastinal irradiation may limit the survival benefit in some cancer patients.