Comparison of the impact of early or late developmental cardiac FKBP12 deficiency in the adult mouse heart. Comparison of control, MCK-FKBP, and αMHC-FKBP-deficient mice and the alterations in cardiac structure and function observed at a whole heart and cardiomyocyte level at 3 mo of age. Findings from Hanna et al. (2025) illustrate that FKBP12 expression is crucial at embryonic day E9 as cardiac structure and function are altered in the αMHC-FKBP-deficient mice. These notable cardiac changes are absent in MCK-FKBP-deficient mice lacking FKBP12 expression from embryonic day E13.5. Created with BioRender.