What is the primary therapeutic effect of beta-blockers?

Beta-blockers primarily work by blocking beta-adrenergic receptors in the heart and vascular system, which leads to a reduction in heart rate and contractility. This decrease in heart rate results from the inhibition of sympathetic nervous system stimulation, which is responsible for increasing heart rate during stress or physical activity. By reducing the workload on the heart, beta-blockers help to lower blood pressure as well, making them effective in managing conditions such as hypertension, angina, and certain types of arrhythmias.

In addition to their effects on heart rate and blood pressure, beta-blockers can also have benefits in reducing myocardial oxygen demand, improving exercise tolerance, and providing protective effects post-myocardial infarction. These characteristics of beta-blockers make their primary therapeutic effect focused on the reduction of heart rate and blood pressure, which is why this is the correct answer.