Of all the blood pumped out of your heart, the brain takes 15 percent, but actually the greatest amount, 20 percent, goes to the kidneys. The output of the two must be in balance, every single time, for it all to work correctly. The heart is not really one pump but two: one that sends blood to the lungs and one that sends it around the body. Blood enters through the atria (Latin for 'entry rooms') and exits via the ventricles (from another Latin word for 'chambers'). It weighs less than a pound and is divided into four simple chambers: two atria and two ventricles.

It just doesn't care about your love life.įor all it does, the heart is a surprisingly modest thing. It has been calculated (and goodness knows how, it must be said) that during the course of a lifetime the heart does an amount of work sufficient to lift a one-ton object 150 miles into the air. Now do that again once every second or so, around the clock, unceasingly, for decades, and see if you don't feel a bit tired. Imagine squeezing a pump the size of a grapefruit with enough force to move a fluid four feet up a tube. If you are standing, your heart is roughly four feet above your feet, so there's a lot of gravity to overcome on the return trip. The heart must pump with enough force not merely to send blood to your outermost extremities but to help bring it all the way back again. That's 1,680 gallons in a day-more gallons pushed through you in a day than you are likely to put in your car in a year. Every hour your heart dispenses around 70 gallons of blood. With such an unrelenting work rate, it is a miracle that most hearts last as long as they do. They are jolts powerful enough to send blood spurting up to three meters if the aorta is severed. Slightly more than once every second, about 100,000 times a day, as many as 3.5 billion times in a lifetime, it rhythmically pulses to push blood through your body-and these aren't gentle thrusts. It has just one job to do, and it does it supremely well: it beats. It is the most single-minded thing within you. The heart is a wondrous organ and fully deserving of our praise and gratitude, but it is not invested even slightly in our emotional well-being. Most curious of all, perhaps, is that we make it the emotional seat of our being, as when we declare that we love someone with all our heart or profess a broken heart when they abandon us. (That symbol first appeared, as if from out of nowhere, in paintings from northern Italy in the early fourteenth century, but no one knows what inspired it.) Nor is the heart where we place our right hand during patriotic moments it is more centrally located in the chest than that.

For a start, it looks nothing like the traditional symbol associated with Valentine's Day and lovers' initials carved into tree trunks and the like.

THE HEART IS the most misperceived of our organs. Last word of British surgeon and anatomist Joseph Henry Green (1791– 1863)

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