What happens to heart rate when isoproterenol is administered?

Isoproterenol is a non-selective beta-adrenergic agonist that primarily stimulates both beta-1 and beta-2 adrenergic receptors. When isoproterenol is administered, its activation of the beta-1 receptors in the heart results in increased myocardial contractility and an elevation in heart rate. This is known as a positive chronotropic effect. The drug mimics the action of endogenous catecholamines like epinephrine, leading to enhanced cardiac output by both increasing heart rate and improving the force of contraction of heart muscles.

Additionally, the stimulation of beta-2 receptors can lead to vasodilation in peripheral vessels, which may also contribute to changes in heart rate due to compensatory mechanisms. Therefore, the net effect of isoproterenol administration is an increase in heart rate, making the correct answer that it increases heart rate.