Just out of curiosity, if I don't take penicillin before my dentist appointments, what are the chances of ? something happening? I had a PDA murmur about two or three years ago, but now it s gone(had surgery ). So what are the chances of something terrible happening? I do take it so don t worry, but I was just wondering. I really don t plan on stopping was just wondering how high of a risk I d be running, trust me I follow directions.