An individual may be able to carry easily forty pounds up a hill and by exerting all his force may carry eighty pounds, but if he habitually carries the eighty pounds, even though the muscles become stronger by exercise the load cannot be again doubled.

The dilatation of the heart which is so important in compensation is fraught with danger, because any weakening of the muscle increases the dilatation, until a point is reached when, owing to the dilatation of the orifices between auricles and ventricles, the valves become incompetent to close them.
When the heart is not able to accomplish its work, the effect of the condition becomes apparent by the accumulation of blood within the veins and a less active circulation.

This affects the nutrition and the capacity for work of all the organs of the body, and the imperfect function of the organs may in a variety of ways make still greater demands upon an already overloaded heart.

Other conditions supervene.
The increased pressure within the veins and capillaries due to the impossibility of the blood in the usual amount passing through or from the heart increases the amount of fluid in the tissues.

There is always an interchange between the blood within the vessels and the fluid outside of them; the passage of fluid from the vessels is facilitated by the increased pressure within them, just as pressure upon a filtering fluid increases the rapidity of filtration, and the increase of pressure within veins and capillaries impedes passage of tissue fluid into them.