['Flow propagation velocity (Vp) is a new method of assessing left ventricular (LV) diastolic (D) function that seems to be insensitive to heart rate and preload changes. We hypothesized that Vp <50 cm/s identifies patients with D dysfunction and that Vp provides an assessment of D function when standard Doppler techniques are uninterpretable. We conducted a prospective Doppler echocardiographic assessment of D function in 63 patients undergoing coronary artery bypass graft surgery. Doppler derivatives of mitral inflow and pulmonary vein flow profiles as well as isovolumic relaxation time were compared with Vp before and after cardiopulmonary bypass. A Valsalva maneuver was used to decrease preload. All patients with D dysfunction had Vp <50 cm/s. A Valsalva maneuver did not affect Vp. Vp remained a reliable measure of LV D function when mitral flow profiles could not be determined because of changes in heart rate and rhythm. LV filling patterns did not change significantly after cardiopulmonary bypass. We conclude that Vp is a simple measure of D function during coronary artery bypass graft surgery that correlates with standard, load-dependent Doppler echocardiographic techniques to identify D dysfunction. Vp <50 cm/s identifies abnormal D function in this patient population.'] Does mitral flow propagation velocity identify patients with abnormal diastolic function during coronary artery bypass graft surgery?