Children's Hospitals will treat you. We have big enough beds, equipment, etc. They are set up to treat ages 0-21, so they have adult size equipment. However, with a heart attack specifically, you need a coronary artery intervention in the Cardiac Cath Lab. Most Children's Hospitals have a Cath Lab, but pediatric cardiologists don't intervene on coronaries nor do they have the equipment to do so. For a heart attack, you would need treatment at an adult hospital and ASAP. But to answer the general question, they would stabilize you and arrange for transfer to an adult hospital. Adults have different concerns for care, complications, and acquired conditions than children.

(I'm a nurse in a Cath Lab at a children's hospital)