USMLE Step 3 Drug MOA Practice Test 2025 – All-in-One Exam Prep

In the management of myocardial infarction, beta-blockers play a critical role by blocking beta-adrenergic receptors in the heart. This action helps to decrease heart rate and contractility, leading to a reduction in cardiac workload and oxygen consumption.

By inhibiting the stimulating effects of catecholamines (such as epinephrine and norepinephrine) on the heart, beta-blockers reduce the frequency and strength of heartbeats, which is particularly important during an infarction when the heart muscle is already compromised and in a state of distress. The decreased demand for oxygen and the lower workload allow the heart to use its remaining resources more efficiently, ultimately improving outcomes in patients suffering from acute myocardial infarction.

In contrast, increasing heart rate could worsen ischemia by elevating myocardial oxygen demand, and inhibiting Na+/K+ ATPase activity is not a characteristic action of beta-blockers, as this is more associated with certain types of cardiac glycosides. Similarly, increasing myocardial oxygen consumption would be counterproductive in a situation where the heart is already struggling. Thus, the primary mechanism of action of beta-blockers in this context is their ability to block beta-adrenergic receptors, leading to decreased heart workload and oxygen demand.