Background Radiation-induced heart disease is a complication that may be encountered after radiotherapy (RT) of tumors in the vicinity of the heart. In this study, we aimed to evaluate the effect of RT on the heart, by comparing conventional and tissue Doppler echocardiography parameters obtained before and after RT.,Methods Forty patients who had undergone RT for either lung or left breast cancer were included in the study. ECG, conventional, and tissue Doppler echocardiography were performed before and 4-6 weeks after RT.,Results The mean value of the radiation dose applied to all regions of the heart was calculated as 13.1 +/- 2.2 Gy (maximum 41.7 Gy). The value for the left ventricle was 10.2 +/- 2.0 Gy (maximum 43.6 Gy). A decrease in early transmitral diastolic velocity (E), E/A ratio, EF, E-m, and E-m/A(m), and an increase in E-wave deceleration time, isovolumic relaxation time, isovolumic contraction time, ejection time, and QT(c) were found after RT.,Conclusion We found detrimental effects of RT on systolic and diastolic cardiac functions and the electrical conduction system of the heart. Maximal prevention should be provided for the patients during RT. Coron Artery Dis 23:146-154 (C) 2012 Wolters Kluwer Health vertical bar Lippincott Williams & Wilkins.