The normal<unk><unk>  in the<unk>  allows the impulse that is generated by the sinoatrial node (SA node) of the<unk>  to be propagated to (and stimulate) the myocardium (Cardiac muscle).  The myocardium contracts after stimulation.  It is the ordered stimulation of the myocardium that allows efficient contraction of the<unk> , thereby allowing blood to be pumped throughout the body.
Electrical conduction system of the heart
Cardiac cycle
Coronary circulation
Anatomy of the heart left atrium
Parasympathetic nervous system
Pulmonary stretch receptors
Sympathetic nervous system
Central chemoreceptors