Objective: The distribution of cardiac output to different organs is well described in the mammalian fetus. Chick embryos are not often used in perinatal cardiovascular research and therefore it is not known whether they can serve as an animal model for this purpose. In this study we documented cardiac output distribution in chick embryos at increasing incubation time. Methods: Fertilized eggs from day 10 to 19 with an incubation time of 21 days were studied in 3 increasing incubation time groups (10-13, 14-16 and 17-19 days). For the experiment, the egg was placed in a holder in an incubator. The egg was opened at the air cell and a small vein of the chorioallantoic membrane was catheterized. Twenty thousand fluorescent 15 mu m microspheres in 0.2 ml were injected. After 5 min, the embryo was sacrificed and the different organs were dissected and digested for microsphere isolation and subsequent fluorescence analysis. Results: The chorioallantoic membrane, which is the placenta equivalent of the chick embryo, received a relatively large fraction of the combined cardiac output: 52.08% (interquartile range [IQR] 12.67%) on days 10-13 and 40.95% (IQR 27.24%) on days 17-19. Relatively small fractions were distributed: to the heart 2.03% (IQR 1.58) on days 10-13 and 3.18% (IQR 1.95) on days 17-19, and to the brain 3.20% (IQR 1.80) on days 10-13 and 5.02% (IQR 3.39) on days 17-19. As incubation time advanced, the fraction of the combined cardiac output to the chorioallantoic membrane and yolk-sac decreased significantly in favor of the heart and brain. Conclusion: This distribution shows great similarity to the one found in the mammalian fetus. The chick embryo is an attractive model for perinatal cardiovascular research.