Without evaluating you, I can't say exactly what's happening with you. However, anxiety certainly can cause these events. That said, one of the other things that we see fairly frequently in adolescents is relative dehydration. This causes the heart rate to increase to maintain blood pressure. I recommend making sure that you are taking in 32-48 ounces per day of fluid (water/milk) and a salty snack (pretzels, saltines, pickles), plus not skipping meals AND eliminating any caffeine, which can also cause palpitations plus cause you to urinate more. If you are still having symptoms despite this, you will need to return to your cardiologist to ensure that there's nothing else going on.