A heated yoga room is a controlled environment, not simply a warm one. The variable that matters is the combination of temperature and humidity, and studios manage both deliberately.
Humidity determines whether sweating works
The body's main route for shedding heat during exercise is evaporation of sweat from the skin, which removes heat as the liquid changes state.
Evaporation slows as the air approaches saturation, so in a humid room sweat accumulates and drips without carrying away the heat it was produced to remove.
A room at a given temperature therefore imposes a very different load at low humidity than at high, which is why studios specify both figures rather than temperature alone.
The cardiovascular response comes from heat, not effort
To move heat from the core to the skin, blood is redirected toward peripheral vessels, which reduces the volume available to the working muscles and to central circulation.
Heart rate rises to maintain output under that redistribution, so the same movement sequence produces a higher heart rate in a heated room than in a cool one.
The elevated heart rate reflects thermoregulatory work rather than greater mechanical effort, which is why it should not be read as a more intense workout in the training sense.
Fluid loss is larger and less obvious
Sweat rates in heated practice can be substantial, and losses continue after class while body temperature returns to baseline.
Thirst is an imperfect guide during and immediately after heat exposure, and drinking large volumes of plain water very quickly can itself cause problems by diluting blood sodium.
Sweat carries electrolytes as well as water, which is why replacement across a day of eating normally differs from replacing volume alone in the minutes after class.
Flexibility gains in heat are largely short-lived
Warm tissue is more compliant, so range of motion increases within a heated session and postures reach further than they would cold.
That change is temporary and reflects tissue temperature rather than a lasting adaptation in the tissue itself.
The practical risk is moving past a habitual range under the impression of new capability, since the supporting structures have not gained corresponding control.
Where heat is genuinely contraindicated
Heat exposure interacts with cardiovascular conditions, pregnancy, and a number of medications including some affecting sweating and blood pressure regulation.
Dizziness, nausea, confusion or the cessation of sweating during a heated class are reasons to leave the room, and anyone with a cardiac condition or on such medication needs a clinician's view before practicing in heat.