C57BL/6 benchmark dataset: Embryonic day 12.5. The most common congenital cardiac abnormalities are associated with the defects in cardiac septation and outflow tract development. Specifically, atrial septal defects (ASDs) account for about one third of the cases detected in adults. To address this question it is imperative to get insight into the genes expressed during normal heart development. Timed matings were performed using C57BL/6 mice and pregnant females sacrificed starting at embryonic day (E) 10.5, and then in daily intervals until E14.5. These developmental stages have been selected as they encompass stages of septation of the atrial and ventricular chambers as well as the cardiac outflow tract. Gene expression was further analyzed at E16.5 and E18.5, to monitor changes in gene expression related to maturation of the heart. At stages 10.5 and 11.5, we have removed the rostral and caudal parts of the embryo and subjected the middle part, which includes the heart, for expression analysis. From embryonic day 12.5 on, we isolated embryonic hearts and separated the ventricular from the atrial chambers. Keywords = cardiac development, heart