Good Morning Dixie,
Metoprolol (Toprol) is a beta-adrenergic blocking agent. Beta-blockers work by interfering with the action of adrenaline and its related chemicals.
Beta blockers slow your heart rate, which can prevent the increase in heart rate that typically occurs with exercise. As a result, the usual age-adjusted target heart rate doesn't work for measuring exercise intensity. No matter how vigorously you exercise when taking a beta blocker, you may never achieve your "target."
I am glad you are going to see your physician and do ask about the problems with the tachycardia and how it will be affected by exercise when taking this medication.
I take Inderal and I go by how I feel when exercising not by target heart rates.
Just a little fyi for you and I am sorry you have to be going through so much stress right now.