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Figure 2 Morphological and histological assessment of the cardiac effects of phenylephrine (PE) treatment in transgenic mice with cardiac targeted overexpression of the wild-type _1B-AR (Tg43) and nontransgenic littermate control (NLC) mice. (A) Morphology of two Tg43 littermates that were either phosphate-buffered saline (left) or PE (right) treated for 14 days. The heart of the sham phosphate-buffered saline treated Tg43 mouse is indistinguishable from a phosphate-buffered saline-treated NLC mouse (not shown). However, as shown on the right, PE treatment increases the size of cardiac chambers, including left and right atria in Tg43 mice. (B) Magnified section of a PE-treated Tg43 heart showing an enlarged left atria with the presence of thrombi, which was seen in >60% of the PE-treated Tg43 mice. (C) Masson trichrome stained section of a representative phosphate-buffered saline treated (sham) NLC mouse taken from the left ventricular wall toward the apex. (D) A similar section taken from a PE-treated (14 days) NLC mouse. (E) A stained section from a sham-treated Tg43 mouse showing no fibrosis. (F) Representative left ventricular section from a PE-treated (14 days) Tg43 mouse showing significant deposition of collagen and fibrosis (staining blue), which was seen in all Tg43 animals after PE.