Heart palpitations (pvcs and pacs on 24-hour monitor). on ritalin (methylphenidate) (40mg). doctors say it's anxiety. should i worry about sudden death or heart attack?

No,but feels like it: No, i wouldn't go that far however, it is a scary feeling. It will help if you stop Ritalin (methylphenidate) and see if the palpitations stabilizes. A benign condition can cause pvc's as well called mitral valve prolapse.

Not necessarily: It depends on the degree of arrhythmia, how many and how many in a row mostly. If the doctor says it is nothing, i presume it is read as none in a row and he is mostly right. Try to relax and if the medicine, you can tell is causing the problem, discuss it with your doctor for alternatives.