Female BRAFfl/fl/Cre+/− mice were treated with corn-oil (CO) or tamoxifen in CO (Tx) 4 days before minipumps were implanted to deliver PBS or 40 mg/kg/d phenylephrine in PBS (PE) for 7 d. (A) Representative M-mode echocardiograms taken from short axis views of the heart (upper panels) with analysis of echocardiograms to assess cardiac dimensions (lower panels). Abbreviations: LVID, left ventricle internal diameter; WT, left ventricle wall thickness (posterior plus anterior walls). Measurements were taken at diastole. (B) Haematoxylin and eosin staining of mouse heart sections (upper panels) with assessment of cardiomyocyte cross-sectional area (CSA; lower panel). Images and measurements are from the periphery of the left ventricle. (C,D) Picrosirius red staining of mouse heart sections showing short axis views of the whole heart (C) with enlarged sections (D) from the same views (the red stain shows accumulation of fibrotic material). Representative (average) images are shown for mice treated with CO/PBS (i), Tx/PBS (ii), CO/PE (iii) and Tx/PE (iv). Additional images are shown for the most severe degree of fibrosis with CO/PE (v) and Tx/PE (vi). (E) Quantification of fibrosis. This was scored as: 1 = the least amount of fibrosis; 2 = low level fibrosis; 3 = high level fibrosis in at least one area of the myocardium; 4 = high level fibrosis throughout the myocardium (half scores were used). Data are presented as individual values with means ± SEM. Statistical analysis used two-way ANOVA with Holm-Sidak’s post-test. Statistically significant values (P<0.05) are in bold type.