Chronic impairment of cardiac lymph flow was successfully accomplished in 22 dogs after preliminary anatomic studies revealed a feasible surgical technic. The anatomic and surgical details are presented. Gross and microscopic studies were possible in 19 of the operated animals, 3 of which died spontaneously, and 16 of which were sacrificed at varying time intervals between 2 and 16 weeks after surgery. Two of the 19 dogs were completely normal on gross and histologic examination. Abnormalities found in the remaining 17 animals included left and right ventricular subendocardial hemorrhages, increased elastic and fibrous tissue in the left ventricular endocardium, and opacification of the mitral valve leaflets.It is concluded that chronic impairment of cardiac lymph drainage is productive of significant endomyocardial pathology. These observations are considered to be important as possible etiologic mechanisms in endomyocardial fibrosis and endocardial fibroelastosis. The cardiac lymphatics merit continued intensive investigation, inasmuch as they surely have an important role in cardiac physiology and pathology. Their importance may encompass a far broader area than suggested above. They may be related to the so-called nutritional cardiopathies. The fibroplastic effects of serotonin might occur through an effect on the cardiac lymphatics. Impairment of heart lymph flow may be important in endocarditis and myocarditis of certain types, for it is known that chronic lymphatic obstruction predisposes to recurrent inflammation and infection in the affected parts.