Your heart is made up of four chambers — two upper chambers (atria) and two lower chambers (ventricles). The rhythm of your heart is normally controlled by the sinoatrial node (SA node) — or sinus node — an area of specialized cells located in the right atrium. This natural pacemaker produces the electrical impulses that trigger the normal heartbeat. From the sinus node, electrical impulses travel across the atria to the ventricles, causing them to contract and pump blood out to your lungs and body.

Premature ventricular contractions are abnormal contractions that begin in the ventricles. These extra contractions usually beat sooner than the next expected regular heartbeat. And they often interrupt the normal order of pumping, which is atria first, then ventricles. As a result, the extra, out-of-sync beats are usually less effective in pumping blood throughout the body.

Why do extra beats occur?

The reasons aren't always clear. Certain triggers, heart diseases or changes in the body can make cells in the ventricles electrically unstable. Underlying heart disease or scarring may also cause electrical impulses to be misrouted. Premature ventricular contractions may be associated with:

  • Chemical changes or imbalances in the body
  • Certain medications, including common asthma medications
  • Alcohol or illegal drugs
  • Increased levels of adrenaline in the body that may be caused by caffeine, exercise or anxiety
  • Injury to the heart muscle from coronary artery disease, congenital heart disease, high blood pressure or infections (myocarditis)
May. 24, 2011