The use of radiotherapy in the management of malignant tumors causes low or high radiation exposure doses to normal tissues and undesired side effects may occur in early and late period following irradiation. All mediastinal structures, lungs and heart can exposure to total therapeutic dose during radiation therapy for thoracal or mediastinal malignancies such as Hodgkin disease and breast cancer. While early deaths following irradiation are caused by primary malignancies among these patients, long-term mortalities are resulted from radiation-induced morphological and functional organ abnormalities. Cardiac changes are the most frequently seen. Significant cardiac anatomical changes occur particularly in pericardium, myocardium, valves and result in severe cardiac dysfunctions after 10 to 20 years following administration of radiation into mediastinal or thoracal areas. The precision of the development of radiation-induced cardivascular complications has increased due to achieving the complete cure of primary tumor and to the extended survival time of irradiated cases by using advanced radiotherapy and adjuvant chemotherapy modalities. Early detection of radiation-induced morphological changes leading to cardiac dysfunction offers the possibility for early intervention such as administration of cardiovascular drugs and/or cardiac surgery in order to reduce or delay severe irreversible late complications.