The pacemaker of the heart is known as ........

The nature of the valves in the heart is:

Chordae tendinae

$A$: The cardiac impulse which originates from $SA$ node in mammalian heart cannot spread directly from atria to ventricles.
$R$: In mammalian heart there is no continuity between cardiac muscle fibres of atria and those of ventricles except $AV$ bundles.

$A$ pacemaker is one that influences the

Which of the following organs contains all four types of tissues?