New York State Emergency Medical Technician (EMT) Practice Exam

What may occur if the heart beats too rapidly regarding cardiac output?

1. A rapid heart beat causes a decrease in the strength of cardiac contractions

2. The volume of blood returning to the heart is insufficient with fast heart rates

3. More blood is pumped from the ventricles than the atria

4. There is not enough time between contractions for the heart to refill completely

The correct answer is: There is not enough time between contractions for the heart to refill completely

When the heart beats too rapidly, one significant consequence is that there may not be enough time between contractions for the heart to refill completely. This is crucial for maintaining effective cardiac output. During the diastolic phase of the cardiac cycle, the heart chambers (the atria and ventricles) fill with blood. A rapid heart rate shortens the duration of this diastolic phase, which can limit the amount of blood that fills the ventricles before the next contraction. If the ventricles do not fill adequately, they cannot eject enough blood during systole, leading to a decrease in stroke volume and, consequently, overall cardiac output. In summary, the rapid heart rate hampers the heart’s ability to adequately fill and pump blood, which can significantly affect circulation and lead to symptoms like dizziness, weakness, or decreased tissue perfusion. Understanding this mechanism highlights the importance of maintaining a healthy heart rate for optimal cardiac function.