My Doctor Recommended Metoprolol ER 50 Mg, For My Heart

My doctor recommended Metoprolol ER 50 mg, for my heart (skipping beats) He said my heart is strong and I don't need to do anything, but this medication would make me feel better and would make my heart stronger, but I have a choice to not take anything. But after picking up this medication, the warnings scare me. If I don't need to take anything, why am I taking something that could kill me if I stop taking it? I am a 70 year old male. and still working as a mechanic.