Background Cardiovascular variables,including stroke volume index,cardiac output index,Smith-Madigan inotropy index and systemic vascular resistance index,are common indexes to monitor critical patients in inten-sive care unit (ICU).A decrease in CO ＞50％ compared with the initial measurement is associated with mortality in preterm neonates with sepsis.But the diagnostic value of these indexes on infected premature infants were less understood before.This study was aimed to evaluate the diagnostic values on infection of premature infants.Methods This was a prospective observational study that included 22 early preterm neonates with proven infec-tion and 16 controls with possible infection.These preterm infants were admitted to neonatal intensive care unit(NICU) from November 2015 to December 2016.Stroke volume index,cardiac output index,Smith-Madigan in-otropy index and systemic vascular resistance index were measured both in healthy time and early stage of prov-en or possible infection.Clinical characteristics and laboratory data were collected.Results Compared with con-trols,the change of stroke volume index (△ SVI) (P=0.001,95％ CI:-2.506 to-0.691),the change of cardiac out-put index (△ CI) (P＜0.001,95％ CI:-0.537 to-0.202),the change of Smith-Madigan inotropy index (△ SMII) (P=0.002,95％ CI:-0.113 to-0.027) and the change of systemic vascular resistance index (△ SVRI) (P=0.002,95％CI:61.186 to 264.756) were more obvious among preterm infants with infection.△ CI had an area under the re-ceiver operating characteristic (ROC) curve of 0.722 (P＜0.001,95％ CI:0.628 to 0.816) for differentiating infect-ed infants from controls.Above a cutoff level of 0.313 L/(min· m-2),△ CI had a sensitivity of 66.7％ and a speci-ficity of 77.1％.The participants were divided into high △ CI group[＞0.313 L/(min· m-2)]and normal △ CI group[≤0.313 L/(min· m2)]according to the cut-off value.Compared with the normal △ CI level group,higher stroke volume index (P＜0.001,95％ CI:1.647 to 3.294),Smith-Madigan inotropy index (P＜0.001,95％ CI:0.025 to 0.110) as well as lower levels of systemic vascular resistance index (P=0.002,95％ CI:-396.834 to-221.444)were observed in the high △ CI group.Binary logistic regression demonstrated that premature patients with high-er increase of CI were associated with the infection (OR:3.080,P=0.026).Conclusions CI,SVI,SVRI and SMII changed obviously in the preterm infants of less than 34 weeks gestation with infection.The increased CI was associated with the infection of preterm patients.CI was expected to be an independent prognostic predictor of infection for preterm infants.