Thanks for your question!
Atherosclerosis is a condition of the arteries which can be quite dangerous. What happens is lipids (or fats) that are in your blood can start accumulating in the walls of the arteries, just like dirt gets accumulated in a pipe. They form what’s called an atheroma plaque. This limits the amount of blood that can circulate through that artery. If the artery is in the heart, making sure the muscle gets oxygen, when it get’s blocked, the part of the heart that gets oxygen from that artery dies very quickly and you have what we call a heart attack.
Hope that answers your question!