<p>Left ventricle (LV) systolic dysfunction, which has been observed in pediatric patients with cancer even prior to chemotherapy, is associated with adverse cardiac events on short-term follow-up. Left atrium (LA) function is pivotal in LV filling and output. Our aim was to evaluate LA function and dimensions before starting chemotherapy in children with cancer, compared to controls.&#xa0;This retrospective cross-sectional study assessed echocardiographic LA function in asymptomatic children with cancer before starting chemotherapy and normal controls. LA function was assessed during the reservoir phase (LASr) denoting LA filling, the passive emptying conduit phase (LAScd) and the active atrial contraction booster phase (LASbo) of the LA strain curve. LV diastolic functional parameters, mitral valve early filling maximum velocity (E), atrial filling maximum velocity (A) and tissue Doppler imaging (E’ and A’) were concurrently measured.&#xa0;The pre-chemotherapy (<i>n</i> = 79) and control (<i>n</i> = 80) groups had comparable gender and age at echocardiogram and similar LASr (39.0% ± 9.2% vs. 39.0% ± 9.1%, <i>p</i> = 0.99). However, LAScd was significantly lower (23.1% ± 11.3% vs. 28.6% ± 8.6%, <i>p</i> &lt; 0.05) and was compensated by increased LASbo function (15.9% ± 11.2% vs. 10.4% ± 7.5%, <i>p</i> &lt; 0.05) in the pre-chemotherapy group, compared to controls.&#xa0;Our data demonstrating abnormalities in LA functional strain parameters in children with cancer, prior to chemotherapy, are novel and perplexing. These LA strain abnormalities may be associated with cancer related systemic effects or inflammatory cytokine release, though the exact mechanisms require further investigation.</p>