How do I know my tachycardia is cured if im on metoprolol. I recently found out I was anemic and I think that is the reason why I am experiencing high heart rate. My resting hr is 85-100 as soon as I walk or brush my teeth it can go up to 130, stairs maybe 150. I am now taking iron supplements twice a day per doctors order. How long until my heart rate goes back to normal assuming its due to anemia?