Temperature Exposure and Cardiovascular Conditions

Urgent help comes first

Chest pain, a racing or irregular heartbeat that does not settle, severe shortness of breath, fainting or confusion during or after cold or heat exposure needs emergency help. In the United States call 911 or the local emergency number. [1] This page is general information, not medical advice. It gives no temperatures, times or schedules, and it is not a clearance to try anything. Do not stop or change a heart or blood-pressure medicine because of this page.

Why the heart is part of the story

Cold and heat both change heart rate, blood pressure and blood flow, quickly. The British Heart Foundation explains that the heart works harder moving through water than on land, and the colder the water, the harder it must work. [2] It describes entering very cold water as able to cause a cold shock with a faster heart rate, higher blood pressure and shortness of breath. [2] It also says cold water can raise stress hormones, increasing the risk of abnormal heart rhythms and possibly cardiac arrest. [2]

For heat, a study of older adults in Japan found that a 1 degree Celsius rise in skin temperature during a hot bath went with a higher systolic blood pressure and pulse rate. [3] That is an observation in baths, not a measure of risk by itself.

What the research says, by exposure

This page uses plain evidence labels. Established means consistent findings from good studies. Promising but limited means early or small studies. Insufficient evidence means not enough to judge. Evidence of harm means good data show risk.

Cold-water immersion and swimming. Researchers have proposed "autonomic conflict" as a mechanism: submersion can activate two opposing nervous-system responses at once, and this may explain the heart rhythm problems seen in cold-water submersion in healthy volunteers. [4] They suggested this may, in some vulnerable people, be responsible for deaths wrongly ascribed to drowning or hypothermia. [4] That is a hypothesis, labeled promising but limited as an explanation, not a settled fact. A case report described sudden submersion in cold water as able to provoke a heart attack, in people with coronary disease and also in young people with normal coronary arteries. [5] A review of winter swimming said people with known or hidden cardiovascular conditions may be more susceptible to adverse effects such as arrhythmias. [6]

The same winter-swimming review said that for people in good general health who build up gradually, it seems to bring cardiovascular and other benefits, and that more prospective studies are needed. [6] The British Heart Foundation likewise says cold-water swimming can improve blood pressure and blood fats in people in good general health, and that people with a heart condition should talk with their doctor or nurse specialist first. [2]

Saunas. A review of the sauna literature called sauna bathing well tolerated by most healthy adults and said it is safe for most people with stable angina or an old heart attack. [7] It listed unstable angina, a recent heart attack and severe aortic stenosis as contraindications, meaning conditions in which sauna bathing should not be used. [7] It also noted that some findings on blood pressure and heart failure need more data. [7] The same paper dates from 2001, so it should be read as background, not current guidance.

Large Finnish cohort studies link frequent sauna bathing with fewer cardiovascular deaths, but they cannot show cause and effect. See Temperature Exposure and Longevity Claims. A review specifically on sudden cardiac death described the evidence as uncertain. [8]

Related pages

• Temperature Exposure Safety: Cold Shock, Fainting and Burns
• Hydrotherapy Safety
• Cold and Heat Exposure