Final answer:
The electrical excitation for a heart beat starts in the sinoatrial (SA) node and spreads through the heart using the atria, atrioventricular (AV) node, bundle of His, and Purkinje fibers.
Step-by-step explanation:
The electrical excitation for a heart beat starts in the sinoatrial (SA) node, which is located near the wall of the right atrium. Electrical charges spontaneously pulse from the SA node, causing the two atria to contract. From the SA node, the electrical impulse spreads to the atria, then to the atrioventricular (AV) node, and further to the bundle of His and the Purkinje fibers. This coordinated spread of electrical signals enables the rhythmic contractions of the heart.