Heart rate variability (HRV)
HRVHeart rate variability is the natural beat-to-beat variation in the time between heartbeats, used as a window into the balance of the autonomic nervous system.
Higher variability generally reflects greater parasympathetic, or rest-and-digest, influence, while lower variability accompanies sympathetic activation during stress, pain or exertion. In dogs it is recorded with electrocardiogram electrodes or wearable chest monitors and analyzed over minutes using time-domain and frequency-domain measures. Researchers studying canine stress often collect it alongside heart rate, cortisol and behavior scores during controlled stressors such as car rides or separation.
Interpretation requires care: breed, age, fitness, breathing pattern, movement and underlying heart disease all influence the numbers, and a change in variability does not by itself show that a dog feels calmer. Veterinary cardiologists also use it to assess heart conditions. Heart rate variability has been measured in canine cannabidiol stress studies, and its findings should be weighed together with behavioral and other physiological data.