Morphological changes to heart after X-ray irradiation of rats at 6 months and 6 weeks of age. Morphological changes to heart 270 days after 8.0 Gy X-ray irradiation. Panel A: Heart sections stained with trichrome. Panel B: Measurement of perivascular cardiac collagen content, an index of cardiac fibrosis. Data are mean ± SD, n = 6/group.