I believe the heart is involved because the brain is involved!
I realize everyone has a different perspective on this but this is how my doctor has explained this to me. The autonomic nervous system is haywire with this illness. It controls your heart rate, blood pressure, circulation, breathing...anything that is automatic.
"What someone with autonomic dysregulation or (dysautonomia) feels on a daily basis is constantly changing and unpredictable. The most common symptoms of dysautonomia is a fast heart rate (not in proportion with the amount of exertion), shortness of breath, dizzy/lightheaded, weak, fatigued/exhausted and having difficulty concentrating or memory loss.
There are many other common symptoms that may be felt on a daily basis that include: orthostatic hypotension (blood pressure plummets upon standing), chest discomfort/pain, anxiety, feeling like going to pass out, actually passing out (syncope), and palpitations (irregular heartbeat).
Some people with dysautonomia have more gastrointestinal related symptoms than others. The common symptoms seen are nausea, vomiting, bloating, abdominal pain, diarrhea, and constipation. One of the other systems that can be affected includes the urinary system with varying bladder dysfunction. Dysautonomia often can also cause headaches/migraines, sleep disorders, hypoglycemia, and myofascial and neuropathic pain.
There are other highly life altering and bothersome side effects that include: heat/cold intolerance, excessive or loss of sweating, blurry vision, tremulousness, exercise intolerance, blood pooling, and noise/light sensitivity.
When feeling highly symptomatic during an episode of intense heart rate and/or blood pressure fluctuations, a person may have a variety of symptoms, including getting overheated and flush, dizzy/lightheaded, blurry vision, nauseous, about to pass out, they can't think straight, and shaky." [from:Health and Wellness, author: AJW]
Mood swings, including irritability are also a part of this. For a full list go to: