Question

fill in the blank question
a decrease in heart rate and blood pressure results when drugs such as propranolol block or inhibit receptors in the heart.

Explanation:

Propranolol is a beta - blocker. Beta - adrenergic receptors ($\beta$ - receptors) in the heart, when stimulated, increase heart rate and contractility. When these receptors are blocked (by drugs like propranolol), the heart rate and blood pressure decrease.

Answer:

$\beta$ - adrenergic