To estimate the preload reserve in response to an increase in afterload in patients with old myocardial infarction, the relation between the Doppler echocardiographic inflow velocity pattern and left ventricular end-diastolic pressure was investigated during isometric handgrip exercise testing. The study population consisted of 16 normal subjects and 40 patients with old myocardial infarction. The 40 patients were subdivided into two groups according to left ventricular end-diastolic pressure at rest: group I (22 patients), less than 18 mm Hg; group II (18 patients), 18 mm Hg or more. At rest, the ratio of peak velocity in atrial contraction phase to peak velocity in early diastolic filling phase (A/E) was significantly higher in the patients with old myocardial infarction than in normal subjects; values in the two subgroups of myocardial infarction did not differ significantly. The A/E ratio and left ventricular end-diastolic pressure increased significantly during exercise in group I. Conversely, the change in left ventricular end-diastolic pressure during exercise in group II was significantly greater than that in group I, and was associated with a decrease in the A/E ratio. Thus, an atrial compensatory mechanism operated effectively in response to the increase in afterload in patients with a normal left ventricular filling pressure, whereas this compensatory mechanism deteriorated in patients with elevated left ventricular filling pressure due to a limited preload reserve.