BMP signals promote proepicardial protrusion necessary for recruitment of coronary vessel and epicardial progenitors to the heart.

The coronary vessels and epicardium arise from an extracardiac rudiment called the proepicardium. Failed fusion of the proepicardium to the heart results in severe coronary and heart defects. However, it is unknown how the proepicardium protrudes toward and attaches to the looping heart tube.