Which of the following is a beta-1 mediated effect on the heart?

• A. Bronchodilation
• B. Increase force of contraction
• C. Vasodilation
• D. Decrease conduction

Answer: (B)

Beta-1 receptors in the heart drive positive inotropy. When these receptors are stimulated, they activate a Gs protein pathway that increases cAMP, which enhances calcium entry and release inside cardiac cells. More calcium available for each heartbeat means stronger contraction. This is the main way beta-1 activity increases the heart’s pumping strength. By contrast, bronchodilation is primarily from beta-2 receptors in the airways, vasodilation is mainly a beta-2 (and other) effect in blood vessels, and decreasing conduction would be a negative dromotropic effect—opposite of what beta-1 stimulation does. So the beta-1 mediated effect on the heart that fits is an increased force of contraction.