The relationship between transmitral Doppler blood flow velocities and atrial contribution to left ventricular (LV) filling was investigated in seven open-chest dogs. At LV filling pressures greater than 15 to 20 mm Hg, LV volume approaches a maximum. Thus we hypothesized that when LV pressure before the onset of atrial systole exceeds this level, the atrial contribution would decrease and the ratio between peak early (E) and atrial-induced (A) mitral velocities would increase. Atrial contribution was measured as LV diameter increase during atrial contraction expressed as a percentage of the total LV diameter change during diastole (sonomicrometry). When left ventricular end-diastolic pressure (LVEDP) was progressively increased from 10 +/- 1 (mean +/- standard deviation) to 28 +/- 3 mm Hg by intravenous saline solution, the atrial contribution decreased from 34 +/- 14% to 8 +/- 10% (p less than 0.001). Concomitantly the A velocity decreased from 39 +/- 7 to 24 +/- 8 cm.sec-1 (p less than 0.01), and the E/A ratio increased from 1.8 +/- 0.3 to 3.6 +/- 1.5 (p less than 0.001). The E/A ratio and the atrial contribution were constant until LVEDP exceeded 17 to 20 mm Hg, at which level marked changes in both parameters were noted. Thus when LV filling pressure was increased, the E/A ratio increased, indicating a filling shift towards early diastole. The reduced atrial contribution during increased preload was explained by the curvilinear shape of the LV pressure-volume curve. At markedly elevated filling pressures, near-maximum LV diameter was achieved before atrial contraction; hence the atrial contribution decreased and the E/A ratio increased.(ABSTRACT TRUNCATED AT 250 WORDS)