part of organ heart A myogenic muscular circulatory organ found in the vertebrate cardiovascular system composed of chambers of cardiac muscle. It is the primary circulatory organ. [database_cross_reference: http://orcid.org/0000-0002-6601-2165][database_cross_reference: http://en.wikipedia.org/wiki/Heart] BTO:0000562 C0018787 EFO:0000815 EHDAA:420 FMA:7088 MESH:D006321 NCIT:C12727 Taxon notes:" the ascidian tube-like heart lacks chambers....The ascidian heart is formed after metamorphosis as a simple tube-like structure with a single-layered myoepithelium that is continuous with a single-layered pericar- dial wall. It lacks chambers and endocardium.... The innovation of the chambered heart was a key event in vertebrate evolution, because the chambered heart generates one-way blood flow with high pressure, a critical requirement for the efficient blood supply of large-body vertebrates... all extant vertebrates have hearts with two or more chambers (Moorman and Christoffels 2003)" http://dx.doi.org/10.1101/gad.1485706 UMLS:C0018787 cardiovascular system