Thrombin insensitive PAR1 transgenic mice demonstrate reduced doxorubicin-induced cardiac fibrosis. Quantification of (A) LV and (B) RVFW, and collagen content from picrosirius red-stained heart sections from Par1^+/+, Par1^-/-, Par1^R41Q, and Par1^R46Q mice at baseline and on day 35 in the chronic model of doxorubicin-induced cardiac injury (n = 3-6/group). (C) Representative micrographs of picrosirius red-stained heart sections from Par1^+/+, Par1^-/-, Par1^R41Q, and Par1^R46Q mice on day 35 in the chronic model of doxorubicin-induced cardiac injury (Scale bars, 50μm). ∗∗∗∗P < .0001; 2-way ANOVA with post hoc Holm-Sidak tests. Data are represented as individual values with the mean and SEM.