Which statement about phenylephrine's effect on heart rate is most accurate?

Which statement about phenylephrine's effect on heart rate is most accurate?

• A. No effect on HR
• B. Reflex bradycardia
• C. Reflex tachycardia
• D. Random HR changes

Answer: (B)

Phenylephrine raises blood pressure by constricting peripheral vessels through alpha-1 stimulation. That rise in arterial pressure activates the baroreceptor reflex, which increases vagal (parasympathetic) activity to the heart and lowers sympathetic outflow. The net effect is a slower heart rate—reflex bradycardia—rather than a direct increase in rate. So, the most accurate statement is that it causes reflex bradycardia. Some patients may have minimal or variable HR responses depending on autonomic tone, but bradycardia is the classic reflex outcome with phenylephrine.

Phenylephrine raises blood pressure by constricting peripheral vessels through alpha-1 stimulation. That rise in arterial pressure activates the baroreceptor reflex, which increases vagal (parasympathetic) activity to the heart and lowers sympathetic outflow. The net effect is a slower heart rate—reflex bradycardia—rather than a direct increase in rate. So, the most accurate statement is that it causes reflex bradycardia. Some patients may have minimal or variable HR responses depending on autonomic tone, but bradycardia is the classic reflex outcome with phenylephrine.