I am a 22 year old female that has episodes of sustained sinus tachycardia in the 140s that last for 10-24 hours at a time which I have had for the last 3-4 years. I have dizziness, lightheadedness, left arm numbness, chest pain and shortness of breath on exertion along with the tachycardia. My cardiologist does not want to treat it because he says "it is just sinus tachycardia" but I am concerned that not treating could and has caused damage to my heart muscle. My normal resting heart rate is 75-80. Shouldn't I be started on a beta-blocker? Should I get a second opinion from another cardiologist?