In atrial fibrillation, erratic electrical impulses can cause the upper chambers of the heart (atria) to fibrillate, or quiver, resulting in an irregular and frequently rapid heart rate. The irregular, sawtooth pattern in the electrocardiogram (EKG, ECG) tracing shows these erratic impulses.

For this non-surgical procedure called catheter ablation, thin tubes called catheters are inserted into a vein, typically in the groin or neck, and threaded through the vein into the heart. A small puncture in the tissue that divides the right and left chambers (septum) allows the catheter to pass into the left atrium.

An electrode at the tip of the catheter sends out radio frequency energy, creating heat that destroys (ablates) the tissue that is causing atrial fibrillation. In this image, the heat is destroying tissue at the base of the pulmonary vein. (The pulmonary veins bring blood back from the lungs to the heart.)

Catheter ablation creates scar tissue that prevents impulses from leaving the pulmonary veins or eliminates the impulses altogether.