Florida State Paramedic Practice Exam

If stroke volume does not change but heart rate decreases, what is the consequence for cardiac output?

1. It increases.

2. It remains the same.

3. It decreases.

4. It becomes irregular.

The correct answer is: It decreases.

Cardiac output is defined as the volume of blood the heart pumps per minute and is calculated by multiplying stroke volume (the amount of blood ejected with each heartbeat) by heart rate (the number of heartbeats per minute). In this scenario, the stroke volume remains unchanged, meaning the amount pumped with each heartbeat does not vary. When the heart rate decreases while the stroke volume stays constant, the overall effect on cardiac output will be a decrease. Specifically, a lower heart rate means that there are fewer beats per minute to deliver blood throughout the body, and thus the total volume of blood pumped in one minute will decline. If you visualize it as filling a glass with a pitcher: if you keep the same rate of pour (stroke volume) but pour less frequently (lower heart rate), the total amount in the glass (cardiac output) will be less. Therefore, a decline in heart rate, while maintaining the same stroke volume, leads to a decrease in cardiac output, reflecting an impaired ability to deliver adequate blood flow to meet the metabolic needs of tissues.