Emergency departments and public-health officials have been warning that very hot weather increases the number of cardiac arrests — and the risk is not limited to the elderly or frail. Heat stress can provoke life‑threatening heart events in people across age groups by increasing cardiovascular strain, dehydration, clotting risk and arrhythmias. As extreme heat events become more frequent and intense with climate change, clinicians, cities and individuals need targeted prevention and response plans.
What the evidence shows
Large epidemiological studies have shown that both high and low ambient temperatures raise overall mortality, and heatwaves in particular are associated with spikes in cardiovascular deaths and out‑of‑hospital cardiac arrests (OHCA). A landmark pooled analysis led by Antonio Gasparrini and colleagues quantified increases in mortality attributable to non‑optimal temperatures and found a substantial share was linked to heat exposure (Gasparrini et al., Lancet, 2015).
Public‑health guidance from agencies such as the World Health Organization and the U.S. Centers for Disease Control and Prevention emphasizes that extreme heat raises cardiovascular risk and can worsen outcomes for people with existing heart disease, and that younger, otherwise healthy people may be affected when exposure is intense (see links below). Heat can accelerate heart rate, lower blood pressure through vasodilation, cause dehydration and electrolyte imbalances, and increase blood viscosity — all of which can precipitate ischemia, arrhythmias or clotting events that lead to cardiac arrest (WHO; CDC).
Why it’s not only an elderly problem
Although older adults and people with chronic illnesses remain among the highest‑risk groups, several factors explain why younger and previously healthy people can suffer cardiac arrests during extreme heat:
- Intensity of exposure: prolonged outdoor work, strenuous exercise, or accidental prolonged exposure (for example, being trapped in a hot vehicle) can overwhelm thermoregulation in younger people.
- Medication interactions: common medications for blood pressure, diabetes or mental health conditions can alter heat tolerance and fluid balance.
- Physiologic responses: dehydration, hypernatremia or electrolyte shifts can trigger arrhythmias irrespective of baseline cardiovascular health.
- Occupational and socioeconomic factors: outdoor laborers, athletes, first responders and people without access to cooling are at elevated risk regardless of age.
Clinical and emergency‑system implications
Higher rates of OHCA during heatwaves strain EMS and emergency departments. Heat can also worsen neurological and cardiac outcomes after resuscitation because of metabolic derangements and delayed presentation. Systems should anticipate surges in calls during heat events, preposition resources, and reinforce community first‑responder training (CPR, early defibrillation) and public cooling measures.
Prevention: practical steps for people and communities
Individuals and health systems can reduce risk with layered interventions:
- Personal precautions: stay hydrated, avoid strenuous activity during hottest hours, seek air‑conditioned environments, and check on friends, neighbors and workers exposed to heat.
- Medication review: clinicians should counsel patients on heat risks related to diuretics, beta‑blockers, anticholinergic agents and some psychiatric drugs and advise on dose or timing adjustments when appropriate.
- Workplace protections: enforce heat‑safety policies, provide shaded rest breaks, and adapt work schedules during heatwaves.
- Public‑health measures: heat–health warning systems, cooling centers, urban greening to reduce heat‑island effects, and targeted outreach to vulnerable subpopulations.
Policy context: climate and the predictable rise in heat risk
Climate science indicates that extreme heat events are increasing in frequency, duration and intensity in many regions, raising the baseline risk for heat‑related cardiac events. The Intergovernmental Panel on Climate Change (IPCC) and public‑health bodies recommend integrating climate adaptation — including heat mitigation and emergency preparedness — into health planning (IPCC AR6; WHO).
What clinicians should watch for
Clinicians should maintain a high index of suspicion for heat‑related cardiac problems during hot spells, even in younger patients presenting with syncope, palpitations, chest pain or altered mental status. Rapid correction of fluid and electrolyte abnormalities, temperature control, and early cardiac monitoring can be lifesaving. Public education on recognizing heat‑related warning signs and when to seek emergency care is essential.
Bottom line
Very hot weather increases cardiac‑arrest risk across age groups by imposing cardiovascular strain, promoting dehydration and deranging electrolytes and coagulation. As heatwaves become more common with climate change, a combined approach — individual precautions, workplace protections, emergency‑system readiness and policy interventions to reduce urban heat — is needed to prevent deaths and preserve cardiac‑arrest survival.
Sources and further reading
- Gasparrini A., et al. Temperature and mortality in 13 large European cities: a pooled analysis (Lancet, 2015)
- World Health Organization — Climate change and health
- U.S. Centers for Disease Control and Prevention — Extreme heat
- American Heart Association — Heat and heart health
- IPCC AR6 — Physical science basis for climate extremes
