As the most glorified pump in existence, there is a special place in everyone’s chest for the heart. Never stopping until you shuffle off this mortal coil, in that time yours will beat about two and a half billion times and pump enough blood to fill several oil tankers. The heart is both a remarkable organ and a powerful symbol; it has become deeply rooted in culture and in language, perhaps in ways you never noticed.
For essentially a muscular sack, it seems funny that if my heart beats for you, yours may skip a beat, but if you are cold-hearted to me you may break mine. If you took my advice to heart it might be because you have a kind heart, or perhaps just because u <3 me. We definitely talk figuratively about the heart a lot. We also definitely see our blood-pump in some way as the seat of emotion, even though that is of course the brain – a nice echo of the ancient Egyptians, who mummified the heart of worthy individuals but threw their brain (which they decided was only for producing mucus) away like offal. Perhaps this is because it is the drumbeat of life, perceptible through a lover’s chest, quickening when tension or passion is high and slowing when the world is calm. Your heart has reflected your inner state since you were born as it has done for every human who ever thought about it.
So really it is no great wonder that it is seen as the seat of emotion. With regards to love especially the idea is so pervasive as to explain even why the ring finger is the finger for the ring: A mistaken belief from the time before circulation was understood was that a large vein runs straight from the ring finger to the heart. A greater wonder is how the shape of a heart became ♥, a symbol important enough to have its own Unicode, and a symbol that actually looks very little like a heart. The answer to this is not completely clear, but the symbol was in use as early as the 1400s and features charmingly in a number of early religious manuscripts (normally representing ‘the sacred heart of Christ’ and with various unfriendly looking implements driven through it).
On top of being used metaphorically as the grounding of human emotion, the heart has linguistically sidled into words as well as sayings. If a sound is discordant it acts ‘against the heart’, if two people are in accord it is because their hearts ‘act together’, and perhaps most tellingly, if you can record something you are linguistically pulling it ‘back from the heart’, because ‘cor’ is the Latin for heart. There are many more examples, but not cord or cordon, which comes from Greek and is dishearteningly an entirely different idea.
We tend to think of our double heart as the normal state of affairs, but in fact our ‘double pump’ system with its four chambers and two separate operating pressures – one for the delicate lungs, and one for the large unyielding remainder of the circulation, is a highly derived feature. Fish blood is pumped by a simple arrangement of but a single atrium and a single ventricle. Squids rather bizarrely have three separate hearts – one sort of like ours and two specifically for pumping blood past the gills. However the majority of these marine circulatory systems are, apart from the workings of the heart, similar in principle to our own. For things to get really weird we must look at arthropods like insects and their strange ‘open’ circulatory systems.
In monkeys, dogs, birds, lizards and the like, the heart pumps blood around sealed pipes called veins and arteries, which branch until every cell has a little capillary running very close by to grab nutrients from and dump waste into. Insects, on the other hand, work essentially like a balloon full of blood. Well, in insects blood is actually called haemolymph, and is blue due to the replacement of red haemoglobin with blue haemocyanin (it contains copper instead of iron as an oxygen carrier), but the point stands. Insects have one open body cavity which all cells are near to, and the heart in such creatures essentially stirs the pot, so is less of a pump and more of a waterwheel.
As a fitting end to this quick introduction to things you didn’t realise about hearts, most hearts end after the same number of beats. Think how much quicker a mouse’s heart beats than your own, and how much quicker in turn a fly’s does. As shorter-lived creatures have faster-beating hearts, it turns out that in general any heart, not just yours, will beat about 2 billion times before its owner no longer needs it to. Enjoy the rest of your heartbeats and have an interesting day.