Final answer:
In a healthy heart, a heartbeat begins within an electrical signal from the sinoatrial (SA) node. The SA node is a specialized group of cells located in the right atrium that acts as the pacemaker of the heart.
Step-by-step explanation:
In a healthy heart, a heartbeat begins within an electrical signal from the sinoatrial (SA) node.
The SA node is a specialized group of cells located in the right atrium. It has the highest inherent rate of depolarization in the heart and is known as the pacemaker. It initiates the electrical signal that spreads through the atria, causing them to contract.
After the electrical signal passes through the atria, it reaches the atrioventricular (AV) node where it is briefly delayed. This delay allows the atria to empty their contents into the ventricles before the ventricles contract.