Benign mesenchymoma of the heart in the guinea pig. A report of four cases.

Thirty-six hundred ninety-eight guinea pigs of the Dunkin-Hartley strain from the breeding colony at Fort Detrick were necropsied. Four females had mesenchymomas of the heart. The tumors were similar histologically and were composed of multiple benign mesenchymal tissues which were amalgamated into a single mass. One tumor was composed of fibrous, angiomatous, adipose, cartilagenous, osscous, hematopoietic, myxomatous, and possibly smooth muscle tissues. Smooth muscle and myxomatous tissues were not found in the other tumors. All were benign and probably originated from the primitive mesenchyme of the heart.