['Sepsis is associated with cardiac contractile dysfunction attributed to alterations in Ca handling. We examined the subcellular mechanisms involved in sarcoplasmic reticulum Ca loss that mediate altered Ca handling and contractile dysfunction associated with sepsis.', 'Randomized controlled trial.', 'Research laboratory SUBJECTS:: Male wild type and transgenic mice INTERVENTIONS:: We induced sepsis in mice using the colon ascendens stent peritonitis model.', 'Twenty-four hours after colon ascendens stent peritonitis surgery, we observed that wild type mice had significantly elevated proinflammatory cytokine levels, reduced ejection fraction, and fractional shortening (ejection fraction %, 54.76\u2009±\u20090.67; fractional shortening %, 27.53\u2009±\u20090.50) compared with sham controls (ejection fraction %, 73.57\u2009±\u20090.20; fractional shortening %, 46.75\u2009±\u20090.38). At the cardiac myocyte level, colon ascendens stent peritonitis cells showed reduced cell shortening, Ca transient amplitude and sarcoplasmic reticulum Ca content compared with sham cardiomyocytes. Colon ascendens stent peritonitis hearts showed a significant increase in oxidation-dependent calcium and calmodulin-dependent protein kinase II activity, which could be prevented by pretreating animals with the antioxidant tempol. Pharmacologic inhibition of calcium and calmodulin-dependent protein kinase II with 2.5 µM of KN93 prevented the decrease in cell shortening, Ca transient amplitude, and sarcoplasmic reticulum Ca content in colon ascendens stent peritonitis myocytes. Contractile function was also preserved in colon ascendens stent peritonitis myocytes isolated from transgenic mice expressing a calcium and calmodulin-dependent protein kinase II inhibitory peptide (AC3-I) and in colon ascendens stent peritonitis myocytes isolated from mutant mice that have the ryanodine receptor 2 calcium and calmodulin-dependent protein kinase II-dependent phosphorylation site (serine 2814) mutated to alanine (S2814A). Furthermore, colon ascendens stent peritonitis S2814A mice showed preserved ejection fraction and fractional shortening (ejection fraction %, 73.06\u2009±\u20096.31; fractional shortening %, 42.33\u2009±\u20095.70) compared with sham S2814A mice (ejection fraction %, 71.60\u2009±\u20094.02; fractional shortening %, 39.63\u2009±\u20093.23).'] Does calcium/Calmodulin Protein Kinase II-Dependent Ryanodine Receptor Phosphorylation mediate Cardiac Contractile Dysfunction Associated With Sepsis?