During a sympathetic nervous system response, which heart rate characteristic is expected?

During a sympathetic nervous system response, tachycardia, or an increase in heart rate, is expected due to the activation of the body's "fight or flight" response. The sympathetic nervous system stimulates the release of catecholamines, such as adrenaline, which increase the heart rate by acting on beta-adrenergic receptors in the heart. This physiological response prepares the body for rapid action, providing greater blood flow to muscles and organs that need it most during stressful situations.

This response contrasts with bradycardia, which involves a decrease in heart rate and is typically more associated with parasympathetic activity, particularly through the vagus nerve's influence. Heart rate stability suggests no significant changes in heart rate, and an irregular heartbeat, or arrhythmia, does not directly reflect the expected physiological response of the sympathetic nervous system. In summary, during sympathetic activation, an increase in heart rate, or tachycardia, is the expected outcome, indicating heightened alertness and readiness for physical activity.