Put a monitor on someone in a hot sauna and the heart rate climbs toward 150, the range of moderate-to-vigorous effort on your feet. Passive heat is real cardiovascular work, not rest.
The Finnish numbers are striking: men who used the sauna four to seven times a week had a 63 percent lower risk of sudden cardiac death than once-a-week men. But that is observational, leaning on one cohort, and the one clean randomized trial in adults with coronary disease came back empty. Eight weeks of sauna moved neither blood pressure, arterial stiffness, nor the vessel walls. The one trial that did lower pressure only worked with the sauna bolted onto exercise.
If you have one, use it. It is not a substitute for the walk.
