Neurogenic locus notch homolog protein 1 (Notch 1) functions as a receptor for membrane-bound ligands Jagged1, Jagged2 and Delta1 to regulate cell-fate determination. Upon ligand activation through the released notch intracellular domain (NICD), Notch 1 forms a transcriptional activator complex with RBP-J kappa and activates genes of the enhancer of split locus. Notch 1 affects the implementation of differentiation, proliferation and apoptotic programs. Defects in Notch 1 are a cause of bicuspid aortic valve (BAV), a common defect in the aortic valve in which two rather than three leaflets are present. It is often associated with aortic valve calcification and insufficiency. In extreme cases, the blood flow may be so restricted that the left ventricle fails to grow, resulting in hypoplastic left heart syndrome.