Anti-heart of glass antibodies enable researchers to detect and measure the heart of glass antigen in biological samples. This target is a reported synonym of the HEG1 gene, which encodes heart development protein with EGF like domains 1. This protein is known to function in cardiac tissue development and in utero embryonic development, among other biological roles. The human version of heart of glass has a canonical amino acid length of 1381 residues and a protein mass of 147.5 kilodaltons, although 2 isoforms have been identified. It is reported to be localized in the cell membrane and is secreted of cells and notably expressed in many tissues, such as the prostate and testis. Other names for this target antigen include protein HEG homolog 1 and heart of glass.