Auxotonic Contraction
This is almost an isotonic contraction because, there is some fluctuation towards the end of the contraction. For example, the heart muscle ventricles contract to expel blood into the pulmonary artery and aorta. As the blood flows out, the previous built up load is now decreased and hence less force is required to expel the rest of the blood. Thus the tension is reduced.
Read more about this topic: Isotonic (exercise Physiology)