S1PR1 and persistent truncus arteriosus: Immunostaining of Wheat Germ Agglutinin (WGA), which binds to glycoprotein of the cell membrane, showed that loss of EC‐S1pr1 significantly increased cardiomyocyte cross‐sectional area in the mice following TAC operation (Figure 2D), while cardiac microvessel density was not altered in S1pr1ECKO mice as shown by isolectin‐B4 staining in banded hearts (Figure 2E).