On the cover: The image shows on the left the formation of the pulmonary myocardial sleeves by rapid proliferation of the just-differentiated myocardium (section of an E12.5 embryo stained for BrdU (red), cTnI (blue) and sytoxgreen (green)). On the right is a 3D reconstruction of an E14.5 wild type heart showing the forming pulmonary myocardial sleeve (grey, Nkx2-5-positive myocardium; aqua, Nkx2-5-negative myocardium; red, lumen pulmonary vein; orange, lumen caval veins). See related article, page 902.