Cardiac Fibrosis.

<p><b>A)</b> Picrosirius red staining showed a significant increase of collagen in both the RV & LV in the groups with only pulmonary arterial banding (PAB). Addition of endothelin receptor blocker (PAB+ERB) significantly lowered the amount of collagen in both RV and LV. Magnification ×10. <b>B)</b> Quantitative collagen volume fractions in the RV. PAB increased collagen compared with sham (*p≤0.0001), macitentan decreased collagen compared with PAB (**p≤0.0001) <b>C)</b> Quantitative collagen volume fractions in the LV. PAB increased collagen compared with sham (§p≤0.0001), macitentan decreased collagen compared with PAB (‡ p≤0.0001). Note the scale difference in the collagen content graphs between the RV and LV. Volume fractions in the various groups were analyzed using Adobe Photoshop (n = 4 for the sham group, n = 7 for the PAB group, and n = 11 for the PAB+ERB group). RV: right ventricle, LV: left ventricle, SP: septum, PAB: pulmonary artery banding, and ERB: endothelin receptor blocker.