Mice heterozygous for floxed BRAF^V600E and hemizygous for Myh6-directed tamoxifen-inducible Cre (BRAF^V600E/WT/Cre^MCM/−) were treated with a single dose of 40 mg/kg (i.p.) tamoxifen or vehicle, and maintained for 10 d (A–C) or 6 weeks (D–G). Cardiac function and dimensions were measured by echocardiography. (A and D) Representative M-mode images from short-axis views for individual mice before and after treatment. (B and E) Quantification of echocardiograms represented in panels A and D, respectively. LV, left ventricle; AW, anterior wall; PW, posterior wall; ID, internal diameter; d, diastole; s, systole. C and G, Sections of BRAF^V600E/WT/Cre^MCM/− mouse hearts stained with haemotoxylin and eosin (H&E) or Masson's Trichrome were analysed. Representative images are shown with quantification provided below (C) or in the right panel (G). (F) B-mode images of long-axis views of the heart were used for speckle-tracking strain analysis. Representative images are in the upper panels with cardiac function data in the lower panels. EDV, end diastolic volume; ESV, end systolic volume; EDLVM, end diastolic left ventricular mass; ESLVM, end systolic LV mass. Data are provided as individual points with means ± SEM. Statistical analysis: unpaired two-tailed t-test.