Heart rate

Heart rate is the number of times the heart contracts and pumps blood in one minute, expressed in beats per minute (bpm). At rest, a healthy adult heart rate typically falls between 60 and 100 bpm, with trained athletes often running lower. It is one of the core vital signs — alongside blood pressure, body temperature, and respiratory rate — used to gauge cardiovascular and overall physiological state.

Heart rate responds to a wide range of inputs: physical exertion, emotional arousal, heat, dehydration, and the presence of psychoactive substances. This sensitivity makes it one of the most immediately readable signals of what a substance is doing to the body, which is why it is commonly tracked in harm-reduction contexts.

How it works · its role

The heart's rhythm originates at the sinoatrial (SA) node — a cluster of specialised cells in the right atrium that fires electrical impulses at a natural, self-sustaining pace. That baseline is continuously tuned by the autonomic nervous system, which operates below conscious awareness.

The sympathetic branch (associated with fight-or-flight responses) releases norepinephrine, which accelerates the SA node and raises heart rate. The parasympathetic branch (associated with rest and recovery) releases acetylcholine via the vagus nerve, which slows it. Heart rate at any moment reflects the balance between these two competing signals — which is precisely where many psychoactive substances intervene.

Relevance to substances & effects

Stimulants act on heart rate most directly. Cocaine, amphetamines, and MDMA all activate the sympathetic system strongly, raising heart rate well above a resting baseline. This is often felt as a pounding or racing chest; at high doses or in people with underlying cardiac conditions, it carries genuine cardiovascular risk.

Depressants generally move in the opposite direction. Opioids and alcohol can reduce heart rate, though the relationship varies with dose and individual tolerance. Cannabis presents a more complex picture: it reliably raises heart rate acutely in most users — especially those with little prior exposure — while tolerance tends to blunt this effect over time.

Classic psychedelics such as LSD and psilocybin typically produce modest heart rate increases through mild sympathetic activation. This is rarely clinically significant in otherwise healthy people, but the physical sensation can be disorienting and may amplify anxiety during an intense experience.

Heart rate during substance use cannot always be cleanly attributed to direct pharmacological action. Anxiety, panic, or heightened excitement will raise heart rate through purely psychological pathways, independent of what the compound itself is doing. When interpreting an elevated reading, the emotional state and setting are rarely separable from the chemical cause.