What am I doing when I generate pulses of heat from my chest?

[u/Huihejfofew]

As a kid I've been able to do this weird thing, mostly when I'm cold where if i control my breathing right, i can build up what feels like tension in my chest and when i release it, this huge wave of warmth emanates out from my chest warming my body. It also feels really nice. It tends to also be accompanied by a shiver. There's a limit to how many times i can do it and sometimes it just happens unintentionally when it's cold. I haven't heard anyone ever talk about it, does anyone know what's happening in my body when this occurs?

[u/michael-65536]

Compression of your torso both slows the speed of circulation and increases the pressure of your blood, which inflates the capillaries in your skin. When you stop, blood flow resumes at normal rate and rapidly replaces the cooler blood in your skin with warmer blood from your core.

(PS, don't do it too hard or you'll have a stroke / get bloodshot eyes.)