Why do you have 3 slits in your heart?

Answer 1

I'm unsure of what you mean by slits... I assume you mean either the different chambers or the valves.

The heart is divided into chambers as to allow the oxygenated blood and the deoxygenated blood to stay separated. As well, the different chambers in the heart give the heart two distinct sides, which beat one after another giving us the 'Da-dum' heartbeat that we're so used to.

The valves help to ensure the blood flows in only one direction in the heart. :]

There is also the septum, which is the big divider in your heart - which would be used to created the different chambers. :]