What would a decrease in heart rate likely do to cardiac output?

• A. Increase cardiac output
• B. Decrease cardiac output
• C. Have no effect on cardiac output
• D. Boost blood pressure

Answer: (B)

Cardiac output is defined as the volume of blood the heart pumps per minute, calculated by multiplying heart rate (HR) by stroke volume (SV). A decrease in heart rate generally leads to a decrease in the number of times the heart beats in a given timeframe. While stroke volume can vary independently of heart rate, a significant decrease in heart rate—if stroke volume remains constant—will typically result in a lower cardiac output.

In a healthy heart, if the heart rate diminishes, particularly below resting levels, it is likely that the total volume of blood being circulated throughout the body will also decline, leading to reduced overall oxygen and nutrient delivery to tissues. Although some factors could compensate for a lower heart rate, such as an increased stroke volume due to better filling time, the direct relationship illustrates that a significant drop in heart rate is likely to decrease cardiac output. This understanding aligns with physiological principles of cardiovascular dynamics, emphasizing the importance of both heart rate and stroke volume in regulating cardiac output.