What is the primary effect of beta-blockers on myocardial oxygen supply?

The primary effect of beta-blockers on myocardial oxygen supply is to reduce oxygen demand. Beta-blockers work by blocking the beta-adrenergic receptors in the heart, leading to several physiological changes. When beta-adrenergic receptors are blocked, there is a decrease in heart rate and contractility, which in turn lowers the myocardial oxygen consumption.

By reducing the workload of the heart, beta-blockers prevent anginal episodes in patients with ischemic heart disease. Although this reduction in oxygen demand contributes to the management of angina, it's important to note that this does not directly improve oxygen supply, but rather addresses the balance between oxygen supply and demand, which is crucial in the context of angina management.

In this context, while beta-blockers do not increase heart rate and do not improve oxygen supply significantly, their central role in reducing oxygen demand is why they are a key treatment in managing conditions such as angina pectoris.