We aimed to assess the relationship between the clinical and biochemical parameters of perfusion and superior vena cava (SVC) flow in a prospective observational cohort study of very low birth weight (VLBW) infants. Newborns with congenital heart disease were excluded. Echocardiographic evaluation of SVC flow was performed in the first 24 h of life. Capillary refill time (forehead, sternum and toe), mean blood pressure, urine output and serum lactate concentration were also measured simultaneously. Thirty-eight VLBW infants were examined. Eight patients (21%) had SVC flow less than 40 ml/kg/min. There was a poor correlation between the capillary refill time (in all sites), mean blood pressure, urine output and SVC flow. The correlation coefficient for the serum lactate concentration was r = -0.28, p = 0.15. The median serum lactate concentration was 3.5 (range 2.8-8.5) vs. 2.7 (range 1.2-6.9) mmol/l (p = 0.01) in low flow versus normal flow states. A serum lactate concentration of >2.8 was 100% sensitive and 60% specific for detecting a low flow state. Combining a capillary refill time of >4 s with a serum lactate concentration of >4 mmol/l had a specificity of 97% for detecting a low SVC flow state. Serum lactate concentrations are higher in low SVC flow states. A capillary refill time of >4 s combined with serum lactate concentrations >4 mmol/l increased the specificity and positive and negative predictive values of detecting a low SVC flow state.