We sought to investigate the changes in atrial reservoir, pump, and conduit functions that are associated with increasing degrees of left ventricular filling impairment. In 13 patients with an impaired relaxation type of filling and in 15 with restrictive patterns, the left atrial volume curve was constructed combining Doppler and 2-dimensional echocardiography. Nine normal subjects served as controls. Left atrial reservoir (defined as [maximum − minimum atrial volume] minus the amount of blood flow reversal in the pulmonary veins with atrial contraction), pump (defined by the volume of blood that enters the ventricle with atrial contraction), and conduit functions (defined as left ventricular filling volume − [left atrial reservoir plus pump volume]) were computed and each expressed as a percentage of ventricular filling volume. The atrial reservoir function was higher in the impaired relaxation group than in normal subjects (49 ± 8% vs 38 ± 8%, p <0.01) but markedly lower in the restrictive group (27 ± 8%, p <0.05). The reverse was true for conduit function, exaggerated in restrictive group (54 ± 12% vs 36 ± 11% in normal subjects, p <0.01) but minimized in patients with an impaired relaxation type of filling (14 ± 9%, p <0.001). The atrial pump contributed 19 ± 6% of ventricular filling volume in restrictives, 26 ± 3% in normals (p <0.01), and 38 ± 4% (p <0.001) in the impaired relaxation group. We conclude that increased atrial response to early-stage left ventricular filling impairment is characterized by augmented reservoir and pump functions, according to a Starling mechanism, which becomes hardly effective at end-stage ventricular dysfunction when the limits of the atrial preload reserve are reached. At this stage, conduit in the atrium takes precedence.