- The sinoatrial (SA) node is known as the natural pacemaker of the heart.
- Its primary function is to initiate the heartbeat by generating electrical impulses.
- These impulses spread through the walls of the atria, causing them to contract and push blood into the ventricles.

Option 1, conducting impulses from the atria to the ventricles, is primarily the role of the atrioventricular (AV) node and the bundle of His.

Option 2, delaying electrical signals before ventricular contraction, describes the function of the AV node, which ensures that the atria have ejected blood into the ventricles before the ventricles contract.

Option 4, regulating the force of myocardial contraction, is controlled by other mechanisms including autonomic nervous system input, not the SA node itself.

Thus, the SA node's role in generating electrical impulses establishes the rhythmic contractions necessary for effective heart function and maintaining a steady heart rate.

Reference: Ganong's Review of Medical Physiology, 26th Edition, Chapter 16/Cardiac Physiology