Assertion (A): Mammalian heart is called myogenic heart.

Reason (R): Heartbeat is regulated by a specialized muscle bundle (pacemaker) in mammals.

Mammalian heart is called myogenic heart because in them the setting of rhythm is done by specialized muscle bundles called pacemaker. they are highly specialized for conducting and generating the impulses. The heart muscles contract and relax without receiving impulses from nervous system, thus mammalian heart is called myogenic heart.