Doppler echocardiograms of the tricuspid and mitral valves were recorded with electrocardiogram and respirations in 20 normal children aged 1.5 to 11 years. Four variables of early diastolic left ventricular (LV) filling decreased with inspiration: the peak E velocity (mean decrease 8%, p less than 0.0001), the ratio of E/A areas (mean decrease 12%, p less than 0.001), the peak E/A velocity ratio (mean decrease 14%, p less than 0.005) and the 1/3 area fraction (mean decrease 12%, p less than 0.001). Variables of late active atrial emptying (peak A velocity and A/total area ratio) were unchanged with respiration. There was a significant increase in the right ventricular (RV) peak E (mean increase 26%, p less than 0.0001) and peak A velocities (mean increase 18%, p less than 0.0001) and mean heart rate (5% increase) with inspiration. The enhancement of RV filling was similar for early and late diastolic filling, since each of the variables generated from their ratios were not significantly changed with inspiration. Inspiration significantly enhances RV venous return, while the LV response to inspiration is a complex interplay among preload, afterload and ventricular interdependence. Assessment of pediatric RV and LV diastolic function should include standardization for phase of respiration.