What is the normal firing rate of the ventricles?

The normal firing rate of the ventricles is typically in the range of 20-40 beats per minute. This low rate reflects the inherent pacing ability of the ventricles when they rely on the Purkinje fibers or other ectopic foci due to a failure of higher pacemakers, such as the atrioventricular (AV) node or the sinoatrial (SA) node. Under normal physiological circumstances, the SA node dictates the heart rate at a much higher rate of approximately 60-100 beats per minute, while the AV node can also pace the heart at a rate of about 40-60 beats per minute if needed. However, if both the SA and AV nodes are not functioning properly, the ventricles then take over as a last resort, leading to this significantly slower rate. This is an important physiological mechanism, as the ventricles ultimately still need to provide a rhythm for blood circulation, even if it is at a reduced rate. Understanding these ranges is crucial for interpreting EKGs in clinical practice.