Which structure transmits the heartbeat signal through the myocardium?

The structure responsible for transmitting the heartbeat signal through the myocardium is the conductive pathways. The heart’s electrical conduction system allows it to contract rhythmically and pump blood effectively.

The sinoatrial node, often referred to as the heart's natural pacemaker, initiates the electrical impulse that causes the heart to beat. However, this node alone does not transmit the signal throughout the myocardium; it triggers the conduction pathways that carry the impulse.

Once the impulse leaves the sinoatrial node, it travels through a series of specialized conductive pathways, including the atrioventricular node, Bundle of His, and Purkinje fibers, effectively coordinating the contraction of the heart muscle. This system ensures that the heart beats in a coordinated manner, allowing for efficient pumping of blood.

Therefore, the conductive pathways encompass the entire system that transmits the pulse generated by the sinoatrial node, leading to the contraction of both the atria and the ventricles, making it the correct answer.