Heart Reflex
Diving reflex
Cold water on the face makes the heart slow down, sends blood to the brain, and holds the breath. Every mammal studied so far has it. You can trigger it with a bowl of cold water.
Everyone
Heart and blood
Heart rate, blood pressure, blood flow, and fainting.
Showing 11 oddities.
The heart and blood vessels adjust constantly to posture, temperature, and emotion, usually faster than you can feel them changing. This region covers the moments where that adjustment becomes obvious.
Vasovagal syncope is the most common reason people faint, when a trigger like pain or heat drops blood pressure suddenly. Seeing stars when standing up happens when blood has briefly pooled in the legs. The diving reflex slows the heart and redirects blood to the brain the moment cold water touches the face.
Every entry here is the circulatory system reacting to something, sometimes usefully and sometimes as an overreaction. None of it is the heart failing. It is the heart and vessels doing their normal job, at a moment when you happen to be paying attention.
Results narrow the list below as you type.
Mainly this region
Heart Trick
Heart rate control
Slowing or speeding up your own heartbeat on purpose, using breath, attention, or training. Breathing can shift it a little within minutes. A few trained people shift it a lot.
No formal count
Heart Reflex
Oculocardiac reflex
Pressure on the eyeball, or a pull on an eye muscle, makes the heart slow down. It matters most during eye surgery, especially in children. It is not a safe way to slow your own heart.
Found in 14–90% of eye muscle operations. Its strength varies a lot.
Heart Involuntary
Seeing stars when standing up
You stand up fast, your vision goes grey or sparkly, and your head feels light for a few seconds. Blood has briefly pooled in your legs. It passes on its own.
Almost everyone, at some time
Heart Reflex
Vasovagal syncope
The most common reason people faint. A trigger like blood, pain, heat, or standing too long makes the vagus nerve slow the heart, and blood pressure drops. The brain briefly runs short of blood and you go down.
About 1 in 3 people faint at least once
Also involves this region
These entries belong to another region first, and touch this one too.
Skin Reflex
Blushing
When you are embarrassed, blood vessels in the face open wide and the skin turns red. You cannot stop it. Darwin called it the most human of all expressions, and no other animal is known to blush from embarrassment.
Everyone
Body Rare ability
CCR5-delta32
About 1% of people of Northern European descent carry two copies of a broken gene that makes them almost immune to the most common form of HIV. A bone marrow transplant from one such donor produced the first cure of HIV.
About 1% of Northern Europeans (two copies)
Organs Reflex
Cold diuresis
Being cold makes you need to urinate. The body pulls blood away from the skin into the core, the heart reads this as too much blood, and the kidneys are told to dump water.
Everyone
Organs Rare ability
Extraordinary breath-holding
Untrained adults usually stop within a minute or two. The best freedivers manage over 11 minutes, and over 29 minutes after breathing pure oxygen. One group of sea nomads has evolved larger spleens for diving.
Trained divers only; no count
Nerves Involuntary
Precordial catch syndrome
A sudden, sharp, stabbing pain near the heart that lasts seconds to a few minutes and gets worse when you breathe in. Doctors count it among the most common causes of chest pain in children and teenagers, and it is harmless.
80–90% of chest pain in young people, once injury is ruled out
Ears Sound
Pulsatile tinnitus
A whooshing or thumping in one ear that keeps time with your pulse. It is usually the sound of blood flowing near the ear. It often has a treatable cause, so get it checked.
Under 10% of people with tinnitus