The frequent involvement of the myocardium and pericardium in infections of bacterial, viral, and rickettsial origin is generally recognized. There remain, however, a good many cases of acute myocarditis and pericarditis of unknown etiology. This poses not only the academic problem of classification but the very practical question of management and prognosis. In the young and middle-aged patient rheumatic fever and tuberculosis and in the middleaged and elderly patient these as well as atypical coronary artery disease have to be considered frequently.

At present, the differential diagnosis is often difficult in spite of careful evaluation of the clinical data, electrocardiograms, roentgenograms, and all conventional laboratory tests, including the unspecific "acute phase reactants," such as erythrocyte sedimentation rate, C-reactive protein, and plasma fibrinogen concentration.

Recently Losner and Volk¹ have observed the persistence of fibrinogen in citrated serum following gross coagulation of whole blood to which a critical dose of heparin