Epigenetic DNA modification involves a temporary chemical change - often by attaching a methyl group to a DNA base chemical – which can activate or silence a gene without permanently altering the genetic DNA composition. This is a crucial molecular process that regulates the structure and function of human cells during development, growth and disease. Our team used bioluminescent tags to visualize dynamic changes in genomic DNA methylation and track cell development in living cells over time. We specifically examined epigenetic DNA modification during the differentiation of stem cells into cardiac cells. This knowledge will help us identify how specific drugs (including those taken during pregnancy) can lead to cardiac abnormalities in children.