Cancer of the heart is an extremely rare disease, and its occurrence is, probably, invariably owing to a highly developed cancerous dyscrasia, or to the proximity of a cancerous formation, as for instance in the mediastinum. The form of cancer affecting the heart appears, as far as we know, to be limited to medullary cancer in its genuine type, or in the form of melanosis. It is developed under and in the external investment of the heart, in any portion of the fleshy walls, or immediately below the endocardium, protruding, according to its size, more or less extensively either inwards or outwards, or even in both directions, in the form of nodules and clumps.

We have observed a case of acute medullary cancer of the heart accompanied by very general acute cancerous formation, in the form of numerous, small, roundish nodules, seated in the innermost layers of the substance of the heart beneath the endocardium, and even upon it, somewhat in the manner of globular vegetations. The above general observations will show that this mode of formation of cancer must be regarded as a highly interesting form of disease of the fibrin.

Cruveilhier (Livr. 29) has described the case of a ragged cancerous tumor seated on the inner surface of the right auricle, and projecting into the cava descendens and the right ventricle. This cancer probably resembled primary cancer of the veins.