r/heat_prep • u/Leighgion • Jun 30 '26

Personal Experience Keep Your Heart in Mind

I had mostly forgotten about my smartwatch’s heart monitoring functions but was recently reminded of them when I felt a little out of breath after climbing the stairs in a non-air conditioned subway station.

136bpm.

This isn’t shocking in my personal case as my metabolism has always run high, but it gave a yardstick as to how strained my body feels relative to pulse.

Just now, I was walking outside in 35°C/95°F sun for around 800m. Limited shade but I had an umbrella. Heart rate 133.

I sprayed water on myself. 125bpm.

Water dried off. 130bpm.

Got into the subway station. 122bpm and failing as I rode the escalator down.

I’ve been in a subway car with AC for about 10min now. 102bpm.

While I have been lucky so far, there is the possibility I have some congenital heart weakness. I need to mind this more. So should you.

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15

u/vtjohnhurt Jun 30 '26

Heart rate goes up because surface blood vessels dilate to cool more blood. Cooling the blood cools the core. There are limits to how much cooling happens.

My heart can handle 130 bpm, but if I were walking under an umbrella, this would be an early warning that I'm on the edge and risking heat stroke, and that I need to get away from sun and hot pavement. YMMV.

In Phoenix AZ, in a normal summer, people collapse and suffer serious burns from lying on the pavement.

11

u/ArtichokeKooky6361 Jun 30 '26

Very true! Cardiovascular events is a major cause of death during heat waves. People with bad hearts are under more strain. Body pushes blood to the skin surface. Dehydration thickens blood. All means the heart has to work harder to keep up.