Induction of vessel and blood specification in zebrafish represses cardiac specification and delimits the heart forming have a common origin in the fish , the common progenitor express cardiac genes of the GATA family but not the blood or endothelial genes. The anterior leteral plate mesoderm in zebrafish is indeed a source of haematopoietic,endothelial , and cardiogenic cells, with the blood and endothelium found in the most rostral region and cardiac tissue in the adjecent more posterior region. The authors proposed that GATA5 and GATA6 are required in both the yolk sac and the endoderm for migration of cardiac progenitors to the midline, but that they are dispensable for the specification of both heart tissue and hemangioblasts. Thus, the role for GATA factor in cardiac cell specification must be allocated within the mesoderm very early in the VE and mesoderm, allowing it to respond to both blood and cardiac-inducing signals. On the other hand, Duncan's laboratory reinvestigated the role of GATAs in cardiomyocyte differentiation after having circumvented the lethelity of the GATA4 or GATA6 deficiency in the VE by tetraploid embryo icomplementation. They genreated a double gata4-/gata6- mouse and showed that these embryos lack the haer, thus pointing to an essential,albeit, redundant role of GATA4 and 6 in the cardiac transcriptional pathway. These findings are in line with the presence of many GATA sites often associated with Smad sites on enhancers of many cardiac genes including the early express Nkx2-5. They are also in agreement with the autonomous and instrumental cardiogenic role of GATA often associated with chromatin modifires in ESCs and embryonic mesoderm. A recent report in zebrafish emphasized the role of FGF in favouring the cardiogenic mesoderm at the expense of the hemangioblast. In this study, Simoes et al. show that the two lineages are mutual antagonists. Nkx2-5 in cardiogenic mesoderm prevents the hemangioblast program by repressing gene expression such as Scl/Tal1 and Etsrp. Similarly, Scl/Tal1 and Etsrp prevent the cardiogenic program. Using a transgenic mouse to isolate Nkx2-5 expressing cells, Caprioli et al. observed an induction of the erythroid molecular program, including Gata1, in the Nkx2-5-null embryos. They showed that Nkx2-5 represses Gata1, which further supports the antagonism between the cardiac and hematopoietic cell lineage. Similarly, Rasmussen et al. used both mouse and ESCs to track haematopoietic and endothelial lineages. The authors employed an Ets-related factor (ER71)-Cre mouse that marks both haematopoietic and endothelial lineages and likely the endocardial but not the myocardial lineage. However, in ER71 null mutant, ER71-Cre x Rosa-EYFP-labelled cells contribute alternatively to heart lineage. Using ESCs and overexpression of ER71 in EBs, the authors showed impairment in cardiac differentiation, thus also revealing an antagonistic action of haematopoiesis on cardiogenesis. Palencia-Desai et al. also recently reported that the absence of Etrsp in zebrafish leads to vascular endothelial and endocardial progenitors redirecting their fate towards the myocardial lineage. Therefore, a combination of studies using mouse and zebrafish highlighted that while sharing an early and common Flk1+ progenitor in the pre-streak embryo, the haematopoietic and cardiac lineages are segregated at gastrulation and are from then on mutually exclusive. ESC might retain bi-potentiality for a longer time and thus caution is required when interpreting in vitro data