The adrenal medulla develops from neural tissue and secretes two hormones, epinephrine and norepinephrine. These two hormones are secreted in response to stimulation by sympathetic nerve, particularly during stressful situations. A lack of hormones from the adrenal medulla produces no significant effects.
While the sinoatrial node typically regulates the heartbeat during normal sinus rhythm, PACs occur when another region of the atria depolarizes before the sinoatrial node and thus triggers a premature heartbeat.
Some other possible signs and symptoms of PVCs: 1  Abnormal ECG. 2  Irregular heart beat. 3  Dyspnea. 4  Dizziness. 5  Feeling your heart beat (palpitations) 6  Feeling of occasional, forceful beats. 7  Increased awareness of your heart beat. 8  Perception of a skipped heartbeat.