Sauna and Heart Failure: What the Research Shows
Key insights
- Most of the heart-failure sauna evidence comes from "Waon therapy" — a specific Japanese protocol of 15 minutes in a 60°C far-infrared dry sauna followed by 30 minutes of rest under a blanket, not a hot Finnish sauna.
- In 34 patients with chronic heart failure, a single sauna session lowered vascular resistance and filling pressures and raised cardiac output, because gentle whole-body warming reduces the heart's preload and afterload.
- Two weeks of daily Waon therapy improved endothelial function (flow-mediated dilation) and lowered BNP, a blood marker of cardiac strain, with symptoms improving in 17 of 20 patients.
- Over five years, patients receiving ongoing Waon therapy had far fewer cardiac events (31%) than matched controls (69%) — a striking result, but from a single small, non-randomised study.
- A 2018 meta-analysis confirmed short-term gains in ejection fraction and reductions in BNP, but rated the overall evidence as moderate-to-insufficient: this is an adjunct to guideline-directed medical care, never a replacement for it.
For decades, a hot sauna was considered off-limits for anyone with a weak heart. The logic seemed obvious: heat raises heart rate and stresses the cardiovascular system, so a failing heart should avoid it. That assumption turned out to be largely wrong — and a body of Japanese research has spent thirty years demonstrating why.
The key is that mild, even warming behaves less like exertion and more like a vasodilator drug. When the whole body is warmed gently, blood vessels open, the resistance the heart pumps against falls, and the pressures inside the heart ease. For a heart that is struggling to move blood forward, that combination can be genuinely helpful rather than harmful.
This article looks specifically at heart failure — a serious clinical condition in which the heart cannot pump efficiently enough to meet the body's needs. If you or someone you care for has heart failure, treat what follows as background for a conversation with a cardiologist, not as a protocol to start on your own.
What "Waon therapy" actually is
Almost all of the clinical heart-failure research uses a defined protocol called Waon therapy ("waon" means "soothing warmth"). A patient sits in an evenly heated far-infrared dry sauna at 60°C for 15 minutes, then lies down and is wrapped in a blanket for a further 30 minutes to maintain the warming effect, often with fluids given to offset sweat losses. This is deliberately mild: 60°C is far cooler than the 80–100°C of a traditional Finnish sauna, and the goal is to raise core temperature by roughly 1°C, not to induce heavy heat stress. That distinction matters, because the cardiovascular trials were done on this gentle protocol — not on high-heat bathing.
How heat could help a failing heart
In heart failure, the heart is working against a system that is often constricted and over-loaded. Gentle whole-body warming widens both arteries and veins. Widening the veins reduces preload — the volume of blood returning to and filling the heart — while widening the arteries reduces afterload, the resistance the heart must overcome to eject blood. Lower preload and afterload mean the heart can move more blood with less effort, the mechanical equivalent of easing off a load 1.
There is a second, slower mechanism. Repeated warming appears to improve the health of the endothelium — the thin lining of the blood vessels that controls how easily they dilate. Better endothelial function, measured as flow-mediated dilation, is thought to be one reason the benefits of Waon therapy accumulate over weeks rather than appearing only during a single session 2.
What the data actually shows
The foundational study came in 1995, when researchers placed catheters in 34 patients with chronic heart failure (average ejection fraction just 25%) and measured their haemodynamics through a single sauna session at 60°C. During and after warming, cardiac output rose, systemic vascular resistance fell, and the elevated filling pressures inside the heart dropped back toward normal. The mitral regurgitation that often accompanies heart failure eased, and the authors concluded that thermal vasodilation could be applied with little risk when appropriately performed 1.
A 2002 study moved from a single session to repeated therapy. Twenty patients in NYHA class II–III heart failure received Waon therapy daily for two weeks. Flow-mediated dilation — a direct measure of endothelial function — improved significantly, BNP concentrations fell, and clinical symptoms improved in 17 of the 20 patients. The pattern suggested the heat was doing more than providing momentary relief; it was improving the underlying behaviour of the blood vessels 2.
The most eye-catching data concern long-term outcomes. In a study of 129 patients with more advanced (NYHA class III–IV) heart failure, 64 received ongoing Waon therapy alongside standard care and 65 matched patients received standard care alone. Over five years of follow-up, cardiac events — hospitalisation for worsening heart failure or cardiac death — occurred in 68.7% of the control group but only 31.3% of the Waon group. That is a large difference, though it comes from a single, relatively small, non-randomised study, so it should be read as promising rather than settled 3.
In 2018, an independent team pooled the trials in a systematic review and meta-analysis. Across the studies that qualified — all of which used infrared Waon-style protocols — sauna therapy was associated with a significant reduction in BNP, a smaller cardiothoracic ratio on chest imaging, and an improvement in left-ventricular ejection fraction. Blood pressure and chamber dimensions did not change significantly, and the authors graded the strength of evidence as moderate to insufficient, calling for larger and longer trials 4.
Realistic expectations and important cautions
The honest summary is that the evidence is encouraging but thin. Most trials are small, conducted by overlapping groups of Japanese investigators, short in duration, and rarely blinded. The 2018 meta-analysis found consistent short-term improvements in cardiac function but could not confirm long-term or mortality benefits with confidence. A larger randomised trial in heart failure with preserved ejection fraction is underway, and it will tell us far more than the current literature can.
Two cautions matter especially. First, the studied protocol is mild — 60°C for 15 minutes with careful rehydration and rest — and these findings do not license someone with heart failure to sit in a 90°C Finnish sauna, where fluid shifts and heart-rate demands are much greater. Second, Waon therapy in every study was layered on top of guideline-directed medical therapy, not used instead of it. Anyone with heart failure, arrhythmia, unstable angina, or significant valve disease should get individual clearance from their cardiologist before using any sauna.
What the protocol looks like in practice
In the trials, the routine is unglamorous and consistent: 15 minutes in an evenly heated far-infrared cabin at 60°C, followed by 30 minutes lying down under a blanket to hold the gentle rise in core temperature, with fluids to replace what is lost through sweat. Sessions ran daily in hospital and then a few times per week as maintenance. The emphasis throughout is on comfort and even, moderate warmth rather than intensity — the therapeutic target is a roughly 1°C rise in core temperature, not the sweat-drenched extremes some associate with sauna culture. For the mechanism behind why regular, moderate heat is easier on the cardiovascular system than occasional intense sessions, see our companion piece on sauna and heart health.
The Contrast Market Perspective
What stands out in this research is how much the results depend on precision: an even 60°C, an accurate 15-minute exposure, and reliable, uniform infrared heat. These were medical protocols where the dose was the treatment, which is exactly why cabin quality, temperature stability, and consistent heat distribution matter. We help people match equipment to their goals and, where health conditions are involved, to work alongside their clinicians rather than around them. If you would like help choosing a sauna suited to gentle, repeatable, well-controlled sessions, Schedule a consultation.
References
Every figure in this article is drawn from the peer-reviewed primary sources listed below. Each links to its record on PubMed.
Footnotes
- Tei C, Horikiri Y, Park JC, et al. (1995). Acute hemodynamic improvement by thermal vasodilation in congestive heart failure. Circulation. PubMed ↩︎
- Kihara T, Biro S, Imamura M, et al. (2002). Repeated sauna treatment improves vascular endothelial and cardiac function in patients with chronic heart failure. Journal of the American College of Cardiology. PubMed ↩︎
- Kihara T, Miyata M, Fukudome T, et al. (2009). Waon therapy improves the prognosis of patients with chronic heart failure. Journal of Cardiology. PubMed ↩︎
- Källström M, Soveri I, Oldgren J, et al. (2018). Effects of sauna bath on heart failure: A systematic review and meta-analysis. Clinical Cardiology. PubMed ↩︎