Increased levels of adrenaline are thought to play a role, often caused by caffeine, exercise or anxiety.
Metoprolol, commonly known as Lopressor is a beta blocker. This medication is used in the treatment of high blood pressure, angina (chest pain, usually caused by lack of oxygen to the heart due to clogged arteries, which can cause PVCs), and heart attack.
I've taken Metoprolol for 6 years, and find it ineffective for treating PVC's, at least for me.