We studied the contribution of phasic left atrial (LA) function to left ventricular (LV) filling during exercise. We hypothesized that reduced LV filling time at moderate-intensity exercise limits LA passive emptying and increases LA active emptying. Twenty endurance-trained males (55 Ϯ 6 yr) were studied at rest and during light-(ϳ100 beats/min) and moderate-intensity (ϳ130 beats/min) exercise. Two-dimensional and Doppler echocardiography were used to assess phasic volumes and diastolic

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... n. LV end-diastolic volume increased from rest to light exercise (54 Ϯ 6 to 58 Ϯ 5 ml/m 2 , P Ͻ 0.01) and from light to moderate exercise (58 Ϯ 5 to 62 Ϯ 6 ml/m 2 , P Ͻ 0.01). LA maximal volume increased from rest to light exercise (26 Ϯ 4 to 30 Ϯ 5 ml/m 2 , P Ͻ 0.01) related to atrioventricular plane displacement (r ϭ 0.55, P Ͻ 0.005), without further change at moderate exercise. LA passive emptying increased at light exercise (9 Ϯ 2 to 13 Ϯ 3 ml/m 2 , P Ͻ 0.01) and then returned to baseline at moderate exercise, whereas LA active emptying increased appreciably only at moderate exercise (6 Ϯ 2 to 14 Ϯ 3 ml/m 2 , P Ͻ 0.01). Thus, the total atrial emptying volume did not increase beyond light exercise, and the increase in LV filling at moderate exercise could be attributed primarily to an increase in the conduit flow volume (19 Ϯ 3 to 25 Ϯ 5 ml/m 2 , P Ͻ 0.01). LA filling increases during exercise in relation to augmented LV longitudinal contraction. Conduit flow increases progressively with exercise in athletes, although this is driven by LV properties rather than intrinsic LA function. The pump function of the LA augments only at moderate exercise due to a reduced diastolic filling time and the Frank-Starling mechanism.