20 people die every day waiting for a heart transplant. Luckily science has found a way to keep people alive without a heart while waiting for a new one. Here’s everything you need to know about artificial hearts.

The first artificial heart was received by Barney Clark in 1982. He only survived for 112 days, but subsequent patients lived longer and longer and now go years on a machine.

The Syncardia Total Artificial Heart is the go-to artificial heart these days. It replaces the left and right ventricles with two bifurcated bladders through which fluid is pumped in and out, forcing the blood up into the atriums like a normal heartbeat.

The fluid is piped into the body through tubes that protrude from the abdomen that lead to a backpack. The backpack carries the pump device and the batteries that power it. Each battery lasts 6 hours.

Another, simpler device is called the Left Ventricular Assist Device, this is a continuously flowing pump that leads blood out of the left ventricle directly into the aorta, meaning people with this device have no pulse.