Rapid-injection indicator-dilution curve After the bolus is injected at
time A, there is a transportation delay before the concentration begins rising
at time B. After the peak is passed, the curve enters an exponential decay
region between C and D, which would continue decaying alone the dotted
curve to t1 if there were no recirculation. However, recirculation causes a
second peak at E before the indicator becomes thoroughly mixed in the blood
at F. The dashed curve indicates the rapid recirculation that occurs when
there is a hole between the left and right sides of the heart.