<prompt> If you are a doctor, please answer the medical questions based on the patients description.Doctor, Ive been experiencing shortness of breath and chest tightness lately. Can you please tell me what could be causing this?  <response>: Based on your symptoms, it seems like you might be experiencing premature atrial contractions PACs. This is a type of heart arrhythmia that causes early contractions in the upper chamber of your heart atria, which can cause the symptoms you described. 