The contractions of
the heart are controlled by chemical (electrolytes- <span style = 'background-color: #dae8f4'>potassium</span>
, calcium, magnesium, sodium, chloride
) impulses, which fire at a rate which controls the beat of
the heart. The cells that create the impulses are called pacemaker cells. IST effects the Sinoatrial Node.
The sinoatrial node (SA node) is responsible for the whole heart's beat and is made up of
cardiac myocyte cells which is muscle fiber.