Although the suction force that moves blood into the left ventricle during early diastole is thought to play an important role in diastolic function, there have been a few studies of this phenomenon in normal children. Suction force is measured as the intraventricular pressure difference (IVPD) and intraventricular pressure gradient (IVPG), which is calculated as IVPD divided by left ventricular length. The purpose of this study was to determine the suction force in infants, children, and adolescents using IVPD and IVPG. We included 120 normal children categorized into five groups based on age: G1 (0–2 years), G2 (3–5 years), G3 (6–8 years), G4 (9–11 years), and G5 (12–16 years). The total, basal, and mid–apical IVPD and IVPG were calculated using color M-mode Doppler imaging of the mitral valve inflow using the Euler equation. The total IVPD increased with age from G1 to G5 (1.75 + 0.51 vs. 2.95 + 0.72 mmHg, respectively; p < 0.001), due to an increase in mid–apical IVPD with constant basal IVPD. Although total IVPG was constant, mid–apical IVPG was larger in G5 than in G1 (0.21 + 0.06 vs. 0.16 + 0.07 mmHg/cm, respectively; p = 0.006). Total, basal, and mid–apical IVPDs were significantly correlated with age and the parameters of heart size and mitral annular eʹ. Mid–apical IVPG correlated with age and e′ positively, but basal IVPG did with age negatively and did not with e′. The suction force increased at the mid–apical segment, correlating with increasing heart size and developing left ventricular relaxation, even after adjustment for left ventricular length.