There are numerous causes of an irregular heart rate, or arrhythmia. According to MedlinePlus, an arrhythmia is any disorder that involves heart rate or rhythm, and may involve a heart rate that's too fast or too slow, or a heart rate that has an irregular pattern. Common symptoms associated with cardiac arrhythmias include skipped beats, dizziness, chest pain and shortness of breath.

Dehydration

According to the Cleveland Clinic, dehydration and electrolyte imbalances in the blood can cause an irregular heart rate known as tachycardia, or the heart beating faster than usual while at rest. Dehydration can be caused by excessive sweating, insufficient water or fluid consumption, along with vomiting and diarrhea. Dehydration can be mild, moderate or severe depending on the volume of fluid lost by the bodyl when severe, it can be life-threatening. According to the Merck Manual, potassium is one of the body's most important electrolytes, and a low potassium level can cause arrhythmias. In people who take digoxin, a drug used to treat heart failure, abnormal heart rhythms may develop when the body's potassium levels are only moderately low.

Coronary Artery Disease

According to the Merck Manual, the most common causes of arrhythmias are heart disorders such as heart valve disorders, heart failures and coronary artery disease. Coronary artery disease is a condition in which plaque builds up on the inside of the coronary arteries' walls, limiting the amount of oxygenated blood getting to the heart. The National Heart Lung and Blood Institute states that atrial fibrillation, or a very fast and irregular contraction of heart's atria or upper chambers, is the most common type of serious arrhythmia, and that coronary artery disease, which damages the heart muscle and limits the heart's ability to conduct electrical impulses, is one of the most common causes of atrial fibrillation. FamilyDoctor.org states that coronary artery disease-induced arrhythmias can be treated and controlled with bypass surgery.

Congenital Heart Defects

According to a 2007 article published in the journal "Circulation," by the time a patient with congenital heart disease becomes a teenager, an irregular heart rate or rhythm typically becomes a central issue in his cardiac management. For some patients with congenital heart defects, arrhythmias are directly associated with the heart's structural malformation, but for most patients with congenital heart disease, arrhythmias are an acquired condition associated with the metabolic byproducts of surgical scars, along with cyanosis, or deficient blood oxygenation, and abnormal heart pressure or volume. The "Circulation" article notes that the following congenital heart defects are associated with cardiac arrhythmias: Ebstein’s anomaly, heterotaxy syndrome, tetralogy of Fallot, congenital aortic stenosis and postoperative mustard, or transposition of the great arteries.