Dear Jack,

When I go to the veterinarian for a checkup, one of the first things they do is listen to my heart. They want to make sure it’s healthy because it pumps blood to my whole body.

I asked my friend Zhaokang Cheng about heart attacks. He’s a scientist at Washington State University. He works on new medicines to help people who have heart attacks or heart disease.

He told me that a heart attack happens when a big blood vessel that delivers blood to the heart gets blocked. Those blood vessels are called coronary arteries.

They get blocked when fatty gunk and other stuff build up on the walls of the arteries. Over time, the buildup can get thicker and harder. It can make the space inside the artery very narrow, so there isn’t much room for blood to get through. Or it can block the artery completely.

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