How does a stent open out when it’s put in there?

When you've got a blocked coronary artery, for example, in the heart, what people used to do was to stick a line in through the top of the leg, into the artery, thread it back to where the heart is, go into the blood vessels supplying the heart and then you inflate a tiny balloon inside the artery.

This opened up the artery by squashing the blockage which was making the artery narrow. When they did that to start with, what would happen is, very quickly the artery would block up, or fur up, again.

So then doctors discovered that the best approach is you if you deploy what's called a stent, which is like a metal scaffold.

Now it's very very tiny when you first put it in and it's threaded over the end of the balloon and when it gets to the right point in the artery where you want to deploy it, you inflate the balloon, which stretches the scaffold. It's almost like it ratchets out and locks in position. It props open the wall of the artery, stopping it constricting again and this should hold the problem area open and make sure it doesn't block again.