Michelle, If they are your good friends they will want to know what is up. Friends are there for each other and you will need their support if you need to have any procedures done in the future. Just be open with them and tell them. By keeping it bottled in they make think you are acting even more "different" than if you tell them the truth.
My son is 6 yrs old and has had 2 open heart surgeries--the first when he was 6 months old and the second when he was 4. He also has a pacemaker. He will be going to kindergarten this fall. Most of his good friends know about his heart and pacemaker and have seen his scars. They treat him as normal as all the other kids. Ben knows his limits and does quite well. We are glad to have the support of his friends and their parents, as well as the teachers and our church family. Hang in there Michelle!