Diabetic heart disease typically features a restrictive/ hypertrophic cardiac phenotype characterised by diastolic dysfunction with preserved systolic performance. Little is known about the early adaptational mechanisms that underpin maintenance of systolic performance in diabetic diastolic dysfunction and how this may contribute to disease progression. This study aimed to evaluate cardiomyocyte contractility in a high-fat diet (HFD) mouse model of diastolic dysfunction. Echocardiography (GE Vivid 9) was performed in 33 wk old male C57Bl/6 mice fed a high-fat diet (HFD, 43% kcal fat, 24 wks duration). Isolated cardiomyocytes (paced 2Hz, 2.0mM Ca 2+ , 37C) were subjected to progressive axial stretch. Sarcomere length/ shortening, tension and intracellular calcium transients (Fura-2AM, 5μM) were simultaneously measured (Myostretcher, Ionoptix). HFD hearts displayed in vivo (22.2±1.4 vs 16.7±1.0 E/E’; pin vitro diastolic dysfunction (0.244±0.039 vs 0.075±0.017 nN/pl/ %cell stretch; p2+ transient amplitude but was correlated with length dependence of Ca 2+ sensitivity (n=17 cells, R 2 =0.4039 p2 =0.8442, p