conus arteriosus

The conus arteriosus is a part of the vertebrate heart. In mammals, it is a conical extension of the right ventricle from which the pulmonary arteries originate. In amphibians and some fish, it's a ventricular extension containing a spiral valve that separates blood flow to the respiratory arteries from blood going to the aorta.1

During embryonic development, the heart begins as a tube. Early structures include the sinus venosus, atrium, ventricle, and the bulbus cordis, which is the embryonic equivalent of the conus arteriosus. In jawless vertebrates like lampreys, the conus arteriosus lacks cardiac muscle and the heart receives oxygen directly from the blood passing through it.234