Cells make decisions about how to reproduce or develop into specialized cell types according to a complex network of proteins that send signals instructing cells to perform different tasks at various time points in their development. Two of these pathways, Notch and beta-catenin, contribute to the regulation of cell growth and fetal development. We found that when Notch interacts with beta-catenin, it results in the degradation of beta-catenin, which in turn regulates the growth of both stem cells and cancer cells. Conversely, when Notch and beta-catenin don’t interact, stem cells expand out of control. Disruption of the balance of these two proteins can lead to a malformed heart during embryonic development.