Standard Doppler indexes of transmitral filling vary in response to alterations in left ventricular (LV) relaxation or preload. To determine whether color M-mode Doppler flow propagation velocity (vp), a new index of LV relaxation, is affected by preload, we obtained LV volumes, standard Doppler filling indexes, and vp in 20 patients at baseline, during Trendelenburg's position, inverse Trendelenburg's position, and after inhalation of amyl nitrite. LV end-diastolic volume decreased from 111 +/- 41 mL at baseline and 116 +/- 43 mL during Trendelenburg's position, to 104 +/- 40 during inverse Trendelenburg's maneuver and 92 +/- 33 mL after inhalation of amyl nitrite (P <.0001). Peak early filling velocity decreased from 79 +/- 19 cm/s and 90 +/- 20 cm/s to 73 +/- 22 cm/s and 64 +/- 20 cm/s, respectively (P < 0.0001). In contrast, no significant changes were found in vp (48 +/- 24 and 50 +/- 26 cm/s vs 48 +/- 25 and 48 +/- 25 cm/s). We conclude that vp is not affected significantly by preload. Thus vp may provide a more reliable and independent assessment of LV relaxation.