The morphologic and hemodynamic datas are compared in 24 patients with mitroaortic valvular cardiopathy. The morphologic study was carried out on left ventricular biopsies and consisted first of all in ultrastructural analysis. Thus, 5 degrees of alterations were determined with regard to myofibrillar and, accessorily, to mitochondrial changes. The microscopic data, especially rarefaction of the Z material on semifine sections stained with Toluidine Blue and the demonstration of phospholipids by staining with acid hematein, are consistent with the ultrastructural gradient. Also, in cases with the most advanced electronic gradient, histoenzymology revealed important anomalies in the activity of the myofibrillar ATPase and of the S.D.H. The correlation between the so-established morphologic gradient and the preoperative hemodynamic data proved satisfying in the majority of cases which points out the interest of the morphologic tests for the appreciation of the functional value of the myocardium.