OBJECTIVE Many pediatric healthcare providers believe that capillary refill time is a measure of perfusion and cardiac output in children. Despite its widespread use, there are no studies examining the relationship of capillary refill time to cardiac output in noncritically ill children. This study examined the inter-rater reliability of capillary refill time and its relationship to hemoglobin and with cardiac output in pediatric patients undergoing cardiac catheterization. METHODS Prospective observational study. METHODS Tertiary care pediatric hospital. METHODS A total of 58 children, ages 0.3-17 yrs, with congenital heart disease undergoing cardiac catheterization. METHODS Two clinicians performed two measurements of capillary refill time in a standardized fashion on 58 children undergoing cardiac catheterization. Cardiac output was determined by the Fick method within 15 mins of the first assessment of capillary refill time (time 1). RESULTS Capillary refill time and cardiac output measurements were obtained in 44 children, and 108 paired measurements of capillary refill time were obtained to assess inter-rater reliability. The mean capillary refill time was 1.2 secs (±0.5 secs), and the mean cardiac output was 3.6 L/min/m (2.2-5.7 L/min/m). The inter-rater intraclass correlation coefficient was 0.12 (time 1) (95% confidence interval -0.15 to +0.37) and was 0.32 (95% confidence interval 0.058-0.54) at the end of the catheterization (time 2). A significant association was noted between average capillary refill time at time 1 and hemoglobin, with higher hemoglobin correlating with longer capillary refill time (p = .015). There was no significant correlation between the average capillary refill time taken at the time of cardiac output measurement (time 1) and measured cardiac output (r = .331, 95% confidence interval for r, .066-.552). CONCLUSIONS We found that the inter-rater reliability of capillary refill time was poor and variable under controlled conditions and capillary refill time was not correlated with cardiac output in anesthetized nonacutely ill pediatric patients undergoing cardiac catheterization. Caution should be used in inferring cardiac output from capillary refill time measurements alone.