Florida State Paramedic Practice Exam

What is the consequence of decreased heart rate on cardiac output if stroke volume remains unchanged?

1. Increased cardiac output

2. Decreased cardiac output

3. Stable cardiac output

4. Variable cardiac output

The correct answer is: Decreased cardiac output

Cardiac output is determined by the formula: Cardiac Output = Stroke Volume × Heart Rate. If the stroke volume remains unchanged and the heart rate decreases, the overall cardiac output will also decrease. This is because a lower heart rate means fewer beats per minute, which directly reduces the total volume of blood pumped by the heart in a given timeframe. For instance, if the heart rate drops from 80 beats per minute to 60 beats per minute while the stroke volume remains constant, the total output in a minute will be less with the lower heart rate. Hence, the consequence of a decreased heart rate, assuming stroke volume is constant, is a decrease in cardiac output. This relationship emphasizes the importance of heart rate in determining how much blood the heart can effectively distribute throughout the body.