Objective To construct a mouse model with conditional knockout of deubiquitinase Otulin gene in the endocardium and to analyze the phenotype ofthe model.Methods A model ofmice with endocardium-specific conditional Otulin gene knockout was constructed with the Cre-loxP technique.The genotypes of Otulin gene knockout mice were determined by using polymerase chain reaction(PCR).Data on the reproduction of the knockout mice was statistically analyzed and the growth and development of the offspring were observed.The Cardiac function of mice was monitored by ultrasound and the changes of cellular components in blood were measured by a fully automatic hematology analyzer.Hematoxylin-eosin(HE)staining was used to analyze the pathological changes in all the tissues and organs ofthe offspring.Results An endocardium-specific Otulin gene knockout mouse model was established.The conditional knockout mice could grow and reproduce normally and the percentage of genotypes of their offspring conformed to Mende's law.Compared with littermate control mice,the conditional knockout mice had smaller body size,lighter weight,significantly enlarged spleens and spiking inflammatory cells in blood.In addition,the tricuspid valve defect and cardiac function were attenuated.Conclusion A mouse model of endocardium-specific Otulin gene knockout has been constructed.These mice show impaired cardiac function and obvious inflammatory response.