What is the normal rate of the SA node?

The normal rate of the SA node, which is the primary pacemaker of the heart, is typically between 60 and 100 beats per minute (BPM). This rate reflects the intrinsic properties of the SA node, which generates electrical impulses that initiate each heartbeat. The SA node's activity ensures that the heart maintains a rhythm that is appropriate for the body's needs under resting conditions.

In healthy individuals, this range allows for adequate cardiac output while ensuring the heart is not beating too slowly or too quickly under normal circumstances. The SA node's function can be influenced by various factors, including autonomic nervous system activity, hormones, and other physiological conditions, but under normal resting conditions, it should reliably generate impulses at a rate within this specified range.

Other choices provided reflect rates that are associated with different pacemaker cells in the heart or pathological conditions. For instance, a rate of 40-60 BPM is typical of the AV node, while 20-40 BPM would be indicative of an escape rhythm originating lower in the conduction system, and 80-120 BPM may be observed during conditions like tachycardia but is not the normal function of a healthy SA node.