Lopressor (Metaprolol) apparently is indeed used to treat PVCs, as a Beta Blocker, it reduces the heart's sensitivity to adrenaline, reduced the forcefulness of the heart's contraction, and reduce the heart rate. /en.m.wikipedia.org/wiki/Metoprolol
In America, drugs whose genetic names end in olol are almost assuredly Beta Blockers, and Metaprolol is and many others are what is known as a selective Beta Blocker. This means that it will have more influence on the heart and less elsewhere than a non-selective Beta Blocker such as Propranolol. Some people with asthma may have more issues with non-selective Beta Blockers since it relaxes the airways somewhat.
Most Beta Blockers are very safe, very well tolerated, and produce few side effects. One advantage is that they can also help you to relax. I have been on one form of Beta Block or another for more than 20 years, and am currently on Atenolol for PVCs.
Whether you take your medication or not is between you and your cardiologist, but keep him/her up to date on your decision.
Was the Holter normal, how many PVCs do you get per day, and is the Stress Test and echo just routine or due to findings from the Holter? Do your PVCs worsen under exertion? These are things to consider as well. Also, what dose did he prescribe?