Multiple echocardiographic techniques have been utilized to quantify systolic function. The shortening and ejection fraction remain the most commonly used and accepted methods. However, these measures are affected by altered loading conditions, and are not applicable when ventricular geometry differs from the prolate ellipsoid typical of a left ventricle. Mitral valve annular acceleration during isovolumic contraction (IVA) has been proposed as a load independent index of left ventricular contractility. However, published values for IVA demonstrating normal function vary. In addition, the value of IVA which may discern impaired systolic function has not been established. The purpose of this study is to determine a threshold IVA value for abnormal left ventricular function in the pediatric population. Structurally/functionally normal control (n = 90) and dilated cardiomyopathy (study = 64) patients were compared for differences in left ventricular: wall stress (WS), velocity of circumferential fiber shortening (VCFc), ejection fraction (EF), ejection force, and pulsed wave-derived medial and lateral wall IVA. No difference in body surface area (p = 0.61) or gender (p = 0.53) was noted. Left ventricular ejection fraction, ejection force, VCFc, and IVA were significantly lower and WS was significantly higher in the study group (p < 0.01). The medial IVA was 1.71 ± 0.89 m/s² for an EF <40%, 1.74 ± 0.70 m/s² for an EF = 40–50%, 2.46 ± 0.89 m/s² for an EF >50%. The lateral IVA was 1.81 ± 1.03 m/s² for an EF <40%, 2.07 ± 0.78 m/s² for an EF = 40–50%, 2.54 ± 0.99 m/s² for an EF >50%. ROC analysis demonstrated a medial IVA of 1.97 m/s² as the cut-off for predicting an EF <50% with a 77% sensitivity of and specificity of 66% (AUC = 0.75, CI = 0.67–0.83, p < 0.01). ROC analysis demonstrated a lateral IVA of 2.31 m/s² as the cut-off for predicting an EF <50% with a 73% sensitivity of and specificity of 63% (AUC = 0.72, CI = 0.63–0.82, p < 0.01). IVA lateral of 1.93 m/s² or less was associated with heart transplant and death. ICC analysis demonstrated some interobserver variability in IVA measurement (0.57–0.65). The normal IVA of the medial and lateral mitral valve annulus measure over 1.97 m/s² and 2.31 m/s², respectively; values less than this cut-off are associated with EF <50%. Despite some problems with reproducibility IVA remains a promising method of screening for diminished ventricular contractility in the setting of abnormal geometry.