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A hallmark of heart failure is impaired cytoplasmic Ca2+ handling of cardiomyocytes. It remains unknown whether specific alterations in nuclear Ca2+ handling via altered excitation-transcription coupling contribute to the development and progression of heart failure.Using tissue and isolated cardiomyocytes from nonfailing and failing human hearts, as well as mouse and rabbit models of hypertrophy and heart failure, we provide compelling evidence for structural and functional changes of the nuclear envelope and nuclear Ca2+ handling in cardiomyocytes as remodeling progresses. Increased nuclear size and less frequent intrusions of the nuclear envelope into the nuclear lumen indicated altered nuclear structure that could have functional consequences. In the (peri)nuclear compartment, there was also reduced expression of Ca2+ pumps and ryanodine receptors, increased expression of inositol-1,4,5-trisphosphate receptors, and differential orientation among these Ca2+ transporters. These changes were associated with altered nucleoplasmic Ca2+ handling in cardiomyocytes from hypertrophied and failing hearts, reflected as increased diastolic Ca2+ levels with diminished and prolonged nuclear Ca2+ transients and slowed intranuclear Ca2+ diffusion. Altered nucleoplasmic Ca2+ levels were translated to higher activation of nuclear Ca2+/calmodulin-dependent protein kinase II and nuclear export of histone deacetylases. Importantly, the nuclear Ca2+ alterations occurred early during hypertrophy and preceded the cytoplasmic Ca2+ changes that are typical of heart failure.During cardiac remodeling, early changes of cardiomyocyte nuclei cause altered nuclear Ca2+ signaling implicated in hypertrophic gene program activation. Normalization of nuclear Ca2+ regulation may therefore be a novel therapeutic approach to prevent adverse cardiac remodeling.