Older age and high morbidity of the society contribute to a growing number of patients with cardiac implantable electronic devices (CIEDs) requiring effective cancer treatment, including radiotherapy (RT). The effect of RT on a CIED may vary depending on the type and physical parameters of radiation, location of the treated lesion, indications for electrotherapy, and the type of CIED. In the most dramatic scenarios, it may cause an irreversible damage to the CIED, with serious clinical consequences. The lack of precise guidelines may limit the access to RT for many patients with CIEDs who would otherwise benefit from the therapy or may lead to a therapy without taking the necessary precautions, which may worsen the prognosis. Therefore, clear and unequivocal recommendations for assessing patient eligibility for RT are aimed at ensuring that adequate precautions are taken as well as at providing patients with concomitant cardiovascular and oncologic diseases with access to safe and effective RT.