Formation and segregation of cell lineages forming the heart have been studied 
extensively but the underlying gene regulatory networks and epigenetic changes 
driving cell fate transitions during early cardiogenesis are still only 
partially understood. Here, we comprehensively characterize mouse cardiac 
progenitor cells (CPCs) marked by Nkx2-5 and Isl1 expression from E7.5 to E9.5 
using single-cell RNA sequencing and transposase-accessible chromatin profiling 
(ATAC-seq). By leveraging on cell-to-cell transcriptome and chromatin 
accessibility heterogeneity, we identify different previously unknown cardiac 
subpopulations. Reconstruction of developmental trajectories reveal that 
multipotent Isl1+ CPC pass through an attractor state before separating into 
different developmental branches, whereas extended expression of Nkx2-5 commits 
CPC to an unidirectional cardiomyocyte fate. Furthermore, we show that CPC fate 
transitions are associated with distinct open chromatin states critically 
depending on Isl1 and Nkx2-5. Our data provide a model of transcriptional and 
epigenetic regulations during cardiac progenitor cell fate decisions at 
single-cell resolution.