What is the major effect of B1 receptor activation in the myocardium?

The major effect of B1 receptor activation in the myocardium pertains specifically to the heart's function. B1 adrenergic receptors are primarily located in the cardiac tissue. When these receptors are activated, they lead to an increase in heart rate (positive chronotropic effect) and an enhancement of myocardial contractility (positive inotropic effect). This means that the heart not only beats faster but also contracts with greater force, increasing cardiac output, especially during situations where the body demands more blood flow, such as during physical activity or stress.

In contrast, vasodilation is typically associated with B2 receptor activity, uterine contraction relates to oxytocin and prostaglandins rather than adrenergic receptors, and bronchodilation is also linked to B2 receptor activation. Thus, the B1 receptors' primary role centers on improving the heart's pumping ability and efficiency, which is why increased heart rate and myocardial contractility is the correct response to the question.