• (a.) Having a single heart, as fishes and amphibians. • (n.) An animal having a single heart.
Mon`o·car'di·an adjective [ Mono- + Greek ... heart.] (Zoology) Having a single heart, as fishes and amphibians. -- noun An animal having a single heart. 
Type: Term Pronunciation: mon′ō-kar′dē-ăn Definitions: 1. Having a heart with a single atrium and ventricle.