Histological assessment of mdx mouse hearts. Representative images of Masson's trichrome staining of mdx mouse hearts at 2 (A), 7 (B), and 10 (C) months of age. D. Quantification of fibrotic tissue at five short-axis levels from apex (A) to midventricle (M), and to base (B). ‡P < 0.01 between 2- and 7-month mdx mice. *P < 0.05, †P < 0.01 between 7- and 10-month mdx mice, respectively.