Which factors can affect heart rate?

The autonomic nervous system activity significantly influences heart rate. This system is divided into the sympathetic and parasympathetic nervous systems, which have opposite effects on heart function. The sympathetic nervous system can elevate heart rate during stress, exercise, or excitement by releasing catecholamines like adrenaline. Conversely, the parasympathetic nervous system slows the heart rate through the release of acetylcholine, particularly when the body is at rest or in a relaxed state. This dynamic interplay allows the body to adapt the heart rate to meet varying physiological demands.

Factors such as dietary intake of sodium, the physical size of the heart, and genetic predisposition can influence cardiovascular health more broadly but do not have the direct, immediate effect on heart rate observed with changes in autonomic nervous system activity. Sodium intake may affect overall blood pressure and fluid balance, which can indirectly influence heart rate over time. The size of the heart can affect cardiac output and potentially heart rate over the long term, while genetic predisposition may set baseline tendencies but does not provide the same immediate modulation as autonomic responses.