Background: A decrease in the supply of ATP from the creatine kinase (CK) system is thought to contribute to the evolution of heart failure. However, previous studies on CK^-/- mice have not revealed overt LV dysfunction. The aim of this study was to employ novel MRI techniques to measure maximal myocardial velocity (v_max) and myocardial perfusion, and thus determine whether subclinical abnormalities in the myocardial phenotype existed in CK^-/- mice, both at baseline and 4 weeks after MI. Methods and results: Myocardial hypertrophy was seen in all CK^-/- mice but EF remained normal. v_max however, was significantly reduced in the CK^-/- mice (wild type 2.32±0.09 vs. CK KO 1.43±0.16cm/s, p<0.05; wild type MI 1.53±0.11 vs. CK^-/- MI 1.26±0.11cm/s, p=ns, p<0.05 vs. baseline). Myocardial perfusion was also lower in the CK^-/- mice (wild type 6.68±0.27 vs. CK^-/- 4.12±0.63ml/g*min, p<0.05; wild type MI 3.97±0.65 vs. CK^-/- MI 3.71±0.57ml/g*min, p=ns, p<0.05 vs. baseline), paralleled by a significantly reduced capillary density (histology). Conclusions: Myocardial function in transgenic mice may appear normal when only gross indices of performance such as EF are assessed. However, the use of a combination of novel MRI techniques to measure myocardial perfusion and mechanics allowed the abnormalities in the CK^-/- phenotype to be detected. The myocardium in CK deficient mice is characterized by reduced perfusion and reduced maximal contraction velocity, suggesting that the adaptive myocardial hypertrophy seen in these mice cannot fully compensate for the absence of the CK system.