The heart's electrical system is quite complex. Electrical rhythms begin as impulses emitted from the sinoatrial node, also known as the heart’s “natural pacemaker.” The impulse then travels across a specific route, or pathway, through the upper chambers of the heart (atria), causing them to contract in unison. After moving through the atria, the impulses reach the atrioventricular (AV) node, which rests between the upper and lower chambers of the heart. There, the signals are reorganized before being transmitted into the lower chambers of the heart, the ventricles, along special bundle of electrical-conducting tissue.

Once the impulses reach the ventricles, they serve as a set of instructions, causing the chambers to contract in a routine and consistent manner. If rhythms are interrupted, delayed or sent down the wrong path, the heartbeat may become abnormal, too fast or too slow. These rhythms are detected by an EKG.

The EKG breaks down each heartbeat into a series of electrical waves that give important information about the heart. Three distinct waves are displayed: the P wave, the QRS complex and the T wave. The P wave is associated with activity in the heart’s upper chambers (atria). The QRS complex and the T wave reflect activity in the lower chambers (ventricles). These three waves are critical in diagnosing a wide variety of heart-related conditions.