Activated calcineurin protein levels are increased in failing human hearts. Human left ventricular protein extracts (400 ug) were immunoprecipitated with excess calmodulin antibody (4 ug) and protein G agarose in calcium-free buffer. Precipitated proteins were then analyzed by western blot to quantify calmodulin and calcineurin protein levels. As activated calcineurin is complexed with calmodulin, these data indicate levels of activated calcineurin. Calcineurin levels were normalized to the amount of immunoprecipitated calmodulin in each reaction (histogram). Western blot analysis of unprecipitated GAPDH levels demonstrates equal integrity of the extracts. The data are quantified as percent activation±sem Significance was demonstrated by an unpaired t-test with software from Instat (GraphPad, San Diego, California).