Cardiac output may decrease if the heart beats too rapidly because:
A. a rapid heart beat causes a decrease in the strength of cardiac contractions.
B. the volume of blood that returns to the heart is not sufficient with fast heart rates.
C. as the heart rate increases, more blood is pumped from the ventricles than the atria.
D. there is not enough time in between contractions for the heart to refill completely.
Answer: D. there is not enough time in between contractions for the heart to refill completely.
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