Background: There has been widespread reporting on predictive dose parameters for cardiac substructures in radiotherapy for non-small cell lung cancer (NSCLC). However, most advanced NSCLC patients are staged as N2-3, and there is a lack of research on the dose distribution, dose contribution and prognosis of the heart in conventional radiotherapy for N2-3 stage NSCLC. Methods: Retrospective analysis of 274 patients of stage N2-3 NSCLC treated with radiotherapy (RT) of prescription dose from 60Gy to 70Gy. Experienced radiation oncologists delineated the cardiac substructures. All patients were categorized according to different lymph node irradiation and tumor spatial locations. Spearman and linear regression were used for variation of dose-volume parameters, as well as the impact of different primary tumor locations and irradiated lymph nodes on the parameters of the entire heart and substructures. Receiver operating characteristic (ROC) curves, Kaplan-Meier, and Cox regression were performed on the influencing factors of adverse cardiac events after radiotherapy and prognosis analysis. Results: There are significant differences in the dose-volume parameters of the whole heart and its substructures. Mean heart doses (MHD),and the mean doses (Dmean) for the left atrium, right atrium, right ventricle, left ventricle and the left anterior descending coronary artery (LAD) were 15.7Gy (range 0.2-30.0Gy), 19.7Gy (range 0.3-55.0Gy), 9.7Gy (range 0.3-59.8Gy), 7.9Gy (range 0.1-48.2Gy), 6.4Gy (range 0.1-52.6Gy) and 5.2Gy (range 0.1-45.0Gy), respectively. The left atrium Dmean has the most significant impact on MHD compared to other substructures (B = 0.418, P < 0.05). Dose-volume parameters of the whole heart and the left atrium were positively correlated with the irradiation of the 7th lymph node region (P < 0.05). MHD and left atrium Dmean for tumors located in the lower region were significantly higher than those in the upper region (P < 0.001). Patients with LAD V30 ≥ 26.9% had a significantly higher risk of mortality compared to those with LAD V30 < 26.9% (P = 0.003, HR = 2.883, 95% CI = 1.436-5.788). Conclusions: With the dose distribution differences among the whole heart and its substructures. We observed the base of the heart received the highest dose, the dose to the left atrium is particularly required attention. The irradiation of different lymph nodes and different primary lesions has an impact on the dose variations of different cardiac structures. LAD V30 is an independent influencing factor of overall survival (OS) for N2-3 stage NSCLC. This study provides considerable information for the dose optimization of cardiac substructure in radiotherapy planning for N2-3 stage NSCLC.