The heart is not a pump.

It is TWO pumps.

You do not have a single circulation.

you have TWO (THREE, if you count the portal venous circulation as a separate circulation).

What the heart does is really very simple. The right side pumps blood around the lungs; the left side pumps it around the rest of the body. Those two circulations never mix, but they are linked. They may sit side by side, but essentially the left side of the heart is a pumping station downstream of the right side.

Each pump – the right side and the left side – is two chambers. An atrium (or ‘hallway’) and a ventricle (or ‘stomach’). There is a valve between the atrium and ventricle on either side, and a valve where the ventricle meets its circulation. The work of the valves is the same as all valves, to make sure that the pumped liquid goes in only one direction.

So, two pumps, each with 2 chambers and 2 valves. Simple.

Except that, for some reason, the heart is twisted around in the body, which makes it look more complex than it really is.

The right side of the heart only has to pump blood through the lungs (where it gets oxygenated), this then returns to the heart (the left side) which pumps it around the body where the oxygen is required for the cells to live.

Because the right side of the heart has relatively little work to do compared with the left, it is not as muscular. In fact, the thickness of the myocardium on the right is only a third that of the left in the normal heart.

What of the heart in the unborn baby? What of congenital abnormalities? More of these in later posts.