Thesis: Radiotherapy is a major treatment for breast cancer; however, it can be associated with a medium to long-term (>5-10 years) increase in the risk of cardiac complications.Specific knowledge regarding the risk of cardiac arrhythmias and conduction disorders among these cardiac complications was limited.In this context, the objective of this work was to study the association between radiotherapy for breast cancer and the risk of developing cardiac arrhythmias and/or conduction disorders, as well as to explore the dose-response relationship between this risk and the absorbed dose by the heart and its sub-structures.Based on medico-administrative data from the French health insurance, this study demonstrated that breast cancer patients treated with radiotherapy had an increased risk of pacemaker implantation and ablation procedures for arrhythmia compared to the general population (SIR=2.18 and 3.55, respectively, p 0.20).This thesis work has thus revealed a potential risk of arrhythmias and conduction disorders after radiotherapy for breast cancer and contributes to opening interesting research directions to better quantify the dose-response relationships with the aim of developing prevention strategies.