It must be emphasized again that right-sided failure is usually secondary to left-sided failure and is therefore associated with pulmonary congestion and dyspnoea. Increasing pressure in the lesser circulation is followed by dilatation and hypertrophy of the right ventricle. Sometimes the heart will fail as a whole and in such cases the clinical manifestations are principally those of right sided failure. Isolated right-sided failure may occur as a result of pulmonary disease, e.g. emphysema, and in certain forms of congenital heart disease, e.g. pulmonary stenosis. When the right ventricle begins to fail, oedema and systemic venous congestion occur. It used to be thought that the occurrence of oedema could be explained on the simple basis of back pressure from a failing right ventricle. Emphasis has now been shifted to the retention of sodium and water by the kidneys. As a result the circulating blood volume is increased and hence also the venous pressure. This determines the occurrence of peripheral oedema. In the same way a rise of pressure in the pulmonary circulation determines the occurrence of pulmonary oedema in left-sided failure. From what has been said it is apparent that an increase in blood volume is an important factor in the causation of oedema while its localization is largely determined by which chamber is failing.
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