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Objectives: Ample clinical and experimental evidence indicated that patients with Alzheimer's disease display a high incidence of cardiovascular events. This study was designed to examine myocardial histology, cardiomyocyte shortening, intracellular Ca2+ homeostasis and regulatory proteins, electrocardiogram, adrenergic response, endoplasmic reticulum (ER) stress and protein carbonyl formation in C57 wild-type (WT) mice and an APPswe/PS1dE9 transgenic (APP/PS1) model for Alzheimer's disease. Methods: Cardiomyocyte mechanical properties were evaluated including peak shortening (PS), time-to-PS (TPS), time-torelengthening (TR), maximal velocity of shortening and relengthening (±dL/dt), intracellular Ca2+ transient rise and decay. Results: Little histological changes were observed in APP/PS1 myocardium. Cardiomyocytes from APP/PS1 but not APP or PS1 single mutation mice exhibited depressed PS, reduced±dL/dt, normal TPS and TR compared with WT mice. Rise in intracellular Ca2+ was lower accompanied by unchanged resting/peak intracellular Ca2+ levels and intracellular Ca2+ decay in APP/PS1 mice. Cardiomyocytes from APP/PS1 mice exhibited a steeper decline in PS at high frequencies. The responsiveness to adrenergic agonists was dampened although β1-adrenergic receptor expression was unchanged in APP/PS1 hearts. Expression of the Ca2+ regulatory protein phospholamban and protein carbonyl formation were downregulated and elevated, respectively, associated with unchanged SERCA2a, Na+-Ca2+ exchanger and ER stress markers in APP/PS1 hearts. Our further study revealed that antioxidant N-acetylcysteine attenuated the contractile dysfunction in APP/PS1 mice. Conclusions: Our results depicted overt cardiomyocyte mechanical dysfunction in the APP/PS1 Alzheimer's disease model, possibly due to oxidative stress. [ABSTRACT FROM AUTHOR]