The Collaborative International Dictionary
Monocardian
Monocardian \Mon`o*car"di*an\, a. [Mono- + Gr. ? heart.] (Zo["o]l.) Having a single heart, as fishes and amphibians. -- n. An animal having a single heart.
Wiktionary
monocardian
a. (context zoology English) Having a heart with a single ventricle.