Abnormalities in the diastolic function of the left ventricular pump are the common determinant and, above all, the earliest manifestation of all forms of chronic left ventricular failure, whether or not the left ventricular systolic function is abnormal. Congestive signs, in particular, are directly related to abnormalities of ventricular filling. Primary diastolic dysfunction is the cause of left ventricular failure in about 40 p. 100 of the cases, but it may also be observed in almost all cardiopathies. In myocardial ischaemia the pressure-volume relation is displaced upwards owing to a slowed down, inhomogeneous and incomplete relaxation. Left ventricular hypertrophy, whether it is due to excessive pressure (arterial hypertension, aortic stenosis) or reflects a primary hypertrophic cardiomyopathy, is associated with a slowing down of ventricular relaxation and a reduction of left ventricular diastolic distensibility, even though the ventricular pump systolic function remains normal for a long time. Outside alterations in the distensibility of the ventricular muscle, ventricular dilatation alters ventricular filling by forcing the ventricle to function on the vertical part of its diastolic pressure-volume relation. Nowadays, the aged hearts is the most frequent cause of heart failure with normal systolic function. In all cases dysrhythmias and atrioventricular desynchronization act as aggravating factors. Treatment is often difficult since positively inotropic drugs or arterial vasodilators frequently have a modest or even deleterious effect.