Cardiac fibrosis in low-TF mice with different levels of TFPI. Mice were euthanized at 6 months of age and hearts analyzed for fibrosis by staining with Masson trichrome. (A) Representative cross sections. Normal myocardium stains red and fibrotic tissue stains blue. (B) Quantitation of the fibrosis was determined using NIH Image Software. Data are presented as mean plus or minus SD from 8 TFPI^+/+/low-TF mice and 7 TFPI^–/–/low-TF mice.