This drug belongs to Class 2A, i.e., a β1-receptor blocker without partial agonist activity (cardioselective β-receptor blocker). It has a selective blocking effect on β1-receptors, no PAA (partial agonist activity), and no membrane stabilizing effect. Its effect of blocking β-receptors is about the same as that of propranolol (PP), and its selectivity for β1-receptors is slightly inferior to that of atenolol. Metoprolol's effects on the heart, such as slowing heart rate, inhibiting cardiac contractility, reducing automaticity, and delaying atrioventricular conduction time, are similar to those of propranolol and atenolol (AT). Its effect of reducing elevated blood pressure and heart rate during exercise testing is also similar to that of PP and AT. Its contraction effect on vascular and bronchial smooth muscle is weaker than that of PP, so its effect on the respiratory tract is also smaller, but still stronger than that of AT. Metoprolol can also reduce plasma renin activity.