Hello! Welcome and thank you for asking on HCM! I would like to have some more information on the antiarrhythmic drug prescribed by your doctor. What are your actual heart rate values while taking metoprolol? I am glad that your cardiac tests have resulted normal. Nevertheless, I would recommend performing further tests to investigate for the possible cause of your irregular heart rate: - complete blood count for chronic anemia - blood electrolytes for possible imbalance - thyroid hormone levels for possible thyroid dysfunction. Meanwhile, I would recommend increasing the dose of metoprolol, instead of adding another drug to your therapy. You should discuss with your doctor on the above issues. Hope you will find this answer helpful! Greetings! Dr. Iliri