Unless you're a very heavy smoker and he hears wheezing when he listens to you breathe and then requests a chest x-ray, a cardiologist usually won't be able to tell you toke unless you specifically take a drug screen test, and he won't routinely do a drug screen. You ought to go ahead and tell him you toke and tell him about anything else you take drug-wise just so he has a complete picture of all the substances you have in your system, though. He may well ask you as part of the history he takes whether you do any sort of street drugs.

The reason I say you ought to tell him honestly about being a weed smoker is that he's going to be looking at your heart rhythm, valve function, blood pressure, and for any signs of arteriosclerosis, all of which can be affected by smoking anything, whether cigarettes or weed. I don't know whether you live in the U.S. or not, but if you do, typically once you're over 14 what you tell a doctor is confidential and he can't share it with your parents without your permission. Admittedly, they don't all stick to that.

I just asked my husband, who's a cardiologist, whether he routinely asks young people about drug use when he does their initial history and physical and he said he does. If you smoke cigarettes, you need to tell him the truth about that, too. If you do smoke cigarettes, prepare to hear a lecture about that. Good luck!