<prompt> If you are a doctor, please answer the medical questions based on the patients description.Sometimes my heart beats really fast and I can feel it thumping in my chest. It feels like my heart is pushing through the chest walls. This normally happens about twice a day and usually occurs when I am sitting. It lasts about 15 minutes and then goes back to my normal rate. Can you tell me the cause of this?  <response>: Hello! Welcome and thank you for asking on Chat Doctor! Your symptoms could be related to anxiety. But, before coming to this conclusion, I would recommend consulting with your attending physician for a careful physical exam and some tests to exclude some other possible causes: - a resting ECG and a cardiac ultrasound-thyroid hormone levels for thyroid dysfunction- complete blood count for anemia-blood electrolytes for electrolyte imbalance- an ambulatory 24-48 hours ECG monitoring to examine your heart rhythm trends for a prolonged time and exclude possible cardiac arrhythmia. Hope to have been helpful! Wishing good health, 