To understand what causes abnormal heart rhythms, one must first have a basic understanding of what causes a normal heart rhythm.

The heart is a large muscle that contracts to pump blood around the body. Each of the heart’s contractions or heartbeats, is triggered by electrical impulses. These electrical impulses are sent from the sinoatrial node (the heart’s natural pacemaker), located at the top of the upper-right chamber of the heart or right atrium. From there, the electrical impulses travel through the upper chambers of the heart (atria), stimulating them to pump blood through the atrial valves to the ventricles. The electrical impulse then travels to the atrioventricular (AV) node, which rests between the upper and lower chambers of the heart (atria and ventricles). From there, they are transmitted to the ventricles via the bundle branches, which stimulate the ventricles to contract, pushing blood through the ventricular valves and out of the heart. The closing of each set of valves as the atria and ventricles contract accounts for the distinctive "lub-dub" sound of a healthy heart. A normal heart will beat approximately 60 to 100 times per minute.

In general, one of the following abnormalies is usually responsible for an arrhythmia:

There are a number of heart-related factors associated with arrhythmias, including:

• Previous heart damage from a heart attack or atherosclerosis (hardening of the arteries).
  
  
• Congenital heart disease or defects (e.g., long syndrome QT, Brugada syndrome, hypertrophic cardiomyopathy).
  
  
• Abnormalities of heart structure or function. These include cardiomyopathy (in which the heart muscle is abnormally enlarged, thickened and/or stiffened) or valvular heart disease.
  
  
• Side effects from medications.

There are other causes of arrhythmias that are not heart-related. These include:

• High stress, anger or hostility.
  
  
• Caffeine consumption (including chocolate).
  
  
• Alcohol consumption.
  
  
• Side effects from prescription medications, including those used to treat arrhythmias.
  
  
• Some over-the-counter medications, including those for coughs, colds or weight loss. This includes certain “natural” or herbal remedies. Guarana, ginseng and ephedra (ma huang) are all stimulants that can increase heart rate, interfere with sleeping, and cause palpitations and other symptoms of arrhythmia.
  
  
• Some illegal drugs. Cocaine, inparticular, over-stimulates the heart, regardless how it enters the body (e.g., snorted, injected, smoked, dissolved on the tongue). This could result in fatal arrhythmias.
  
  
• Sleep disorders, such as insomnia or sleep apnea.

Other risk factors include age, hypertension, diabetes, left ventricular hypertrophy, pulmonary disease and electrolyte abnormalities such as low potassium and magnesium.