Term: atrium endocardium
Name: atrium
Synonyms:
Definition: Cavitated compound organ that receives inflow of deoxygenated blood and delivers it to a muscular cardiac ventricle. Valves are present to direct flow. There are only two chambers present in the fish heart.
Ontology: Anatomy Ontology [ZFA:0000471]

Name: endocardium
Synonyms:
Definition: Layer that lines the lumen of the heart.
Ontology: Anatomy Ontology [ZFA:0001320]