FHOD3 deficiency disrupts sarcomere organization and activates CaMKII signaling in human stem cell-derived cardiomyocytes

• FHOD3 knockout in human embryonic stem cell-derived cardiomyocytes leads to sarcomere disorganization, impaired calcium handling, mitochondrial dysfunction, and reduced contractility. • Transcriptomic analysis reveals downregulation of sarcomere and calcium-handling genes, with enrichment in cardiomyopathy and calcium signaling pathways. • FHOD3 deficiency activates CaMKII signaling via phosphorylation at Thr286, contributing to heart failure progression. • Omecamtiv mecarbil partially restores contractility in FHOD3-deficient cardiomyocytes without affecting calcium handling, suggesting a potential therapeutic strategy.