A novel long non-coding RNA (lncRNA), Braveheart (Bvht), has been defined as a critical regulator of commitment of the embryonic stem cells (ESCs) to cardiovascular lineages. Bvht activates a cardiovascular gene network and functions upstream of mesoderm posterior 1 (MESP1), a master regulator of a common multipotent cardiovascular progenitor. Bvht mediates epigenetic regulation of commitment to a cardiac lineage by interacting with SUZ12, a component of polycomb repressive complex 2 (PRC2). Bvht represents the first lncRNA that defines cardiac cell fate and lineage specificity, linking lncRNAs to cardiac development and disease.