“Saunas are dangerous if you have heart disease.”

The research found this

Finnish and international reviews give similar advice. A 2006 Finnish review found no particular risk in the sauna for people with coronary disease or heart failure whose condition was stable and treated.1Source 1 · ReviewHealth effects and risks of sauna bathingKukkonen-Harjula K, Kauppinen K. International Journal of Circumpolar Health, 2006.Read the paper ↗PubMed ↗ It named four heart-related exceptions: prolonged or unstable chest pain, a heart attack or other severe cardiac event in the past four to eight weeks, severe aortic stenosis and severe drops in blood pressure on standing. A review in the American Journal of Medicine named unstable angina and a recent heart attack among its reasons to stay out, and the Kuopio group's 2024 review adds uncontrolled high blood pressure and severe valve disease.2Source 2 · ReviewBenefits and risks of sauna bathingHannuksela ML, Ellahham S. The American Journal of Medicine, 2001.Read the paper ↗PubMed ↗3Source 3 · ReviewThe multifaceted benefits of passive heat therapies for extending the healthspan: A comprehensive review with a focus on Finnish saunaLaukkanen JA, Kunutsor SK. Temperature, 2024.Read the paper ↗PubMed ↗

Studies of heart patients in the sauna are small. A study in Bern gave two 80°C sauna sessions and a 12°C plunge to 25 men with chronic heart failure or coronary disease and to 12 healthy men. Systolic pressure reached its low point six minutes into the sauna, and nobody had complex heart rhythm problems.4Source 4 · Clinical trialAcute effects of Finnish sauna and cold-water immersion on haemodynamic variables and autonomic nervous system activity in patients with heart failureRadtke T, Poerschke D, Wilhelm M, et al.. European Journal of Preventive Cardiology, 2016.Read the paper ↗PubMed ↗ In Montreal, 16 people with coronary disease tolerated a sauna without symptoms or ECG changes.5Source 5 · Clinical trialSauna-induced myocardial ischemia in patients with coronary artery diseaseGiannetti N, Juneau M, Arsenault A, et al.. The American Journal of Medicine, 1999.Read the paper ↗PubMed ↗ Scans still showed reduced blood flow to the heart muscle in 14 of 15 of them, and the pattern resembled their exercise scans.

The 2006 review also summarizes older Finnish data: 69 patients bathed four to six weeks after a heart attack without harm, and 8% had irregular heartbeats in the sauna against 18% during an exercise test.1Source 1 · ReviewHealth effects and risks of sauna bathingKukkonen-Harjula K, Kauppinen K. International Journal of Circumpolar Health, 2006.Read the paper ↗PubMed ↗ In the largest heart-failure trial, adverse events occurred in 22% of patients given infrared Waon therapy and 15% of controls. The gap wasn't significant, and nobody died.6Source 6 · Randomized trialWaon Therapy for Managing Chronic Heart Failure – Results From a Multicenter Prospective Randomized WAON-CHF Study –Tei C, Imamura T, Kinugawa K, et al.. Circulation Journal, 2016.Read the paper ↗PubMed ↗

Deaths in saunas are rare and cluster in people who already have heart disease. A Kuopio review of sudden cardiac death found that most people who died during or after a sauna had coronary disease, and that alcohol was often a key factor in the case reports.7Source 7 · ReviewIs sauna bathing protective of sudden cardiac death? A review of the evidenceLaukkanen JA, Kunutsor SK. Progress in Cardiovascular Diseases, 2019.Read the paper ↗PubMed ↗ In northern Finland, 2.6% of autopsied sudden cardiac deaths under age 80 happened in a sauna, and so did 5.5% of those at 80 or older.8Source 8 · Case seriesCauses and characteristics of unexpected sudden cardiac death in octogenarians/nonagenariansPuolitaival E, Vähätalo J, Holmström L, et al.. PLOS ONE, 2023.Read the paper ↗PubMed ↗

Some heart medicines interact with the heat. Blood pressure drugs can deepen the fall in pressure after a sauna, and Finnish guidance suggests taking them afterward.1Source 1 · ReviewHealth effects and risks of sauna bathingKukkonen-Harjula K, Kauppinen K. International Journal of Circumpolar Health, 2006.Read the paper ↗PubMed ↗9Source 9 · Web pageSydänsairaus ja saunaTerveyskylä. Terveyskylä, 2021.Read the page ↗ Nitroglycerin patches release more drug in the heat: in one study, blood levels reached 7.3 nmol/L in a sauna against 1.0 to 1.5 on a control day, and 9 of the 12 volunteers had headaches during the study.10Source 10 · Clinical trialIncreased uptake of transdermal glyceryl trinitrate during physical exercise and during high ambient temperatureBarkve TF, Langseth-Manrique K, Bredesen JE, et al.. American Heart Journal, 1986.Read the paper ↗PubMed ↗