Just how is it that you ended up here? Have you had any tests that reveal you have a heart problem? Chest pain does not mean a heart problem. It could be autonomic system issues among other issues. Metaprolol is a blood pressure med and it also can be used in certain heart conditions. You say your heart doctor sent you to this site to get information on your condition?

The mechanism of metoprolol is a cardioselective, beta-1 adrenergic receptor blocker which has the desired effects of reducing heart rate and blood pressure and increasing cardiac output. The metabolism of metoprolol occurs primarily via the CYP2D6 enzyme, with reported estimates of approximately 70–80%. See https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10058912/
Genetic testing of the Cytochrome P450 (CYP) would tell you what kind of metabolizer of CYP2D6 you are. Example I am an "intermediate metabolizer" of 2D6.
Is it possible that this might be an endocrine system problem?