part of develops from ends during starts during heart XAO:0000064 UBERON:0000948 A myogenic muscular organ found in the cardiovascular system. It is responsible for pumping blood throughout the blood vessels by repeated, rhythmic contractions. It is composed of cardiac muscle, which is an involuntary striated muscle tissue found only in this organ, and connective tissue. It is ultimately composed of three chambers (two atria and one ventricle), occupying a ventral position within the chest of the mature tadpole/frog. xenopus_anatomy cardiovascular system heart primordium death viscus cavitated compound organ NF stage 28