PURPOSE: To assess cardiac mortality, coronary artery disease, myocardial dysfunction, and valvular heart disease in women younger than 65 years of age, at least 10 years after adjuvant radiotherapy following mastectomy in early breast cancer. METHODS AND MATERIALS: Ninety women (45-64 years old) with Stage II breast cancer without relapse, included in the South Sweden Breast Cancer Trial (premenopausal arm), with or without adjuvant postoperative radiotherapy +/- cyclophosphamide were examined with myocardial scintigraphy and echocardiography/Doppler, 10-17 years after radiotherapy. Thirty-four patients had been irradiated for left-sided tumors, 33 for right-sided tumors, and 23 patients had not been treated with radiotherapy. The radiotherapy (conventional roentgen, electron beams, and high-energy photon beams combined, in each patient) included the chest wall and the regional lymph nodes, with a specified target dose of 38-48 Gy, administered in daily fractions of 1.9-2.4 Gy, 5 days/week. RESULTS: No cardiac deaths were found among the original 275 patients randomized to adjuvant therapy. In the 90 patients examined, abnormal findings were recorded for ECG (14 patients), exercise test (5 patients), myocardial scintigraphy (6 patients), thickening of valve cusps (14 patients), and mild valvular regurgitation (20 patients). All patients had normal systolic function. Diastolic dysfunction was observed in 6 patients (abnormal relaxation in 4 patients and restrictive filling abnormality in 2 patients). Although no significant differences were found between the 3 study groups, there was a tendency to more abnormal findings after radiotherapy. CONCLUSION: Women younger than 50 years of age at the time of adjuvant radiotherapy following mastectomy in early breast cancer, had no serious cardiac sequelae 13 years (median) later, despite partly old-fashioned radiation techniques.