Heart failure (HF) progression has not been studied in pediatric patients as well as HF in patients with a normal ejection fraction (HFNEF). We aimed to evaluate galactin-3 in children with HFNEF and reduced ejection fraction (HFREF) and its correlation to disease severity and progression. This cross-sectional study involved 45 chronic HF patients taking G1a (23 HFNEF children) and G1b (22 HFREF children) compared to 45 age- and sex-matched controls (G2) subjected to history taking, Ross functional HF classification, conventional and tissue Doppler echocardiographic systolic and diastolic function assessment (FS%, E/A, S _m, E _m/A _m, E/E _m) and laboratory investigations [glomerular filtration rate, serum galactin-3 level (ELISA)]. The results showed that serum galactin was increased in patients compared to controls (p > 0.001); a cutoff value of 3.5 ng/ml was estimated for HF diagnosis HFNEF patients who had higher galactin-3 levels than HFREF patients, but it did not reach statistical significance (p = 0.194). Galactin-3 levels positively correlated to the Ross HF classification (p = 0.01) and E/E _m (p = 0.032) and negatively correlated to FS%, S _m and E _m/A _m (p = 0.028, 0.022, 0.043). Galactin-3 levels were significantly reduced in patients receiving spironolactone (p = 0.049). Galactin-3 can be a tool for chronic HF diagnosis and a marker of disease severity and staging in children with HFNEF and HFREF. The role of spironolactone in reducing galactin-3 in pediatric HF requires further research.