heartbeat science

"Each electrical signal begins in a group of cells called the sinus node or sinoatrial (SA) node. The SA node is located in the right atrium (AY-tree-um), which is the upper right chamber of the heart. (Your heart has two upper chambers and two lower chambers.) In a healthy adult heart at rest, the SA node sends an electrical signal to begin a new heartbeat 60 to 100 times a minute. From the SA node, the signal travels through the right and left atria. This causes the atria to contract, which helps move blood into the heart's lower chambers, the ventricles (VEN-trih-kuls). The electrical signal moving through the atria is recorded as the P wave on the EKG. The electrical signal passes between the atria and ventricles through a group of cells called the atrioventricular (AV) node. The signal slows down as it passes through the AV node. This slowing allows the ventricles enough time to finish filling with blood. On the EKG, this part of the process is the flat line between the end of the P wave and the beginning of the Q wave. The electrical signal then leaves the AV node and travels along a pathway called the bundle of His. From there, the signal travels into the right and left bundle branches. The signal spreads quickly across your heart's ventricles, causing them to contract and pump blood to your lungs and the rest of your body. This process is recorded as the QRS waves on the EKG."