An increase in the left ventricular end-diastolic pressure (LVEDP), resulting from the i.v. administration of blood, a colloid solution or a crystalloid solution, was accompanied by an increase in both the inner:outer left ventricular wall flow ratio and the diastolic myocardial tissue pressure gradient. With a normal left ventricular end-diastolic pressure, the normal inner:outer flow ratio was just above unity and the minimum diastolic myocardial tissue pressure in the subepicardium was twice as high as in the subendocardium. When the left ventricular end-diastolic pressure was raised, the subepicardial tissue pressure rose earlier and to a higher degree than the subendocardial; thus a gradient which encourages subendocardial flow was increased. This paper correlates the changes in diastolic myocardial tissue pressure and in inner:outer flow ratios which occurred when 8 dogs were transfused with blood, 7 with colloid and 7 with lactated Ringer''s solution. Regional diastolic myocardial tissue pressure was measured by the flow-cessation technique and regional flow by radioactive microspheres. The gradient in diastolic myocardial tissue pressure, which is a major contributory factor to adequate subendocardial perfusion under normal conditions, is of even greater importance when LVEDP is raised.