Panic and rapid heartbeat are mainly due to sympathetic nerve excitation.
Sympathetic nerve excitation will occur in the body after a series of hormonal responses, this situation may be physiological, but also may be pathologic.
When emotional excitement, physiological state of the body will occur stress or acute response, agitation of sympathetic nerves adrenal cortex or medullary system of activity response, and then release catecholamines, including epinephrine, norepinephrine, dopamine, etc., can stimulate the heartbeat accelerated, so that the human body has a feeling of panic.
If you have a heart disease, mood changes can also trigger an increase in the local excitability of the heart muscle, which will activate the sympathetic nerves, resulting in a rapid heartbeat and a feeling of panic.
It is recommended that if you suffer from recurrent panic attacks, you should seek medical attention as soon as possible to avoid delaying your condition.