Which two properties work together to create a normal sinus rhythm?

The choice of automaticity and conduction as the correct answer highlights two fundamental properties essential for establishing a normal sinus rhythm in the heart.

Automaticity refers to the heart's ability to generate electrical impulses spontaneously. This is particularly characteristic of pacemaker cells located in the sinoatrial (SA) node, which is the natural pacemaker of the heart. These cells can depolarize without external stimuli, setting the rhythm for the entire heart.

Conduction, on the other hand, pertains to how these electrical impulses propagate through the heart's conduction system, including pathways like the atrioventricular (AV) node, Bundle of His, and Purkinje fibers. Proper conduction ensures that the impulses generated in the SA node effectively travel to the atria and ventricles, leading to coordinated contractions.

When combined, automaticity ensures that the heart can generate impulses, while conduction guarantees that these impulses are transmitted appropriately throughout the heart muscle, resulting in a synchronized and effective heartbeat central to maintaining a normal sinus rhythm.