Impaired coronary artery maturation and disorganized myocardial vasculature in left ventricles of CHF1/Hey2 knockout mice. PECAM (a, b) and αSMA (c, d) immunostaining were performed for E18.5 embryonic hearts. The control left ventricles (a, c; n=7) generally form well-developed coronary arteries with a distinct circumferential αSMA positive smooth muscle layer (arrows). In contrast, mutant ventricles (n = 8) showed dysmorphic vessels with a partially disrupted smooth muscle layer (d, arrows, inset) within a disorganized myocardial vasculature (b, arrowheads). Scale bars = 200 μm.