A particular application of haemoglyphs, whereby a person is imbued with a glyph's properties when it is placed semi-permanently on (or even in) their heart. Until the Advanced Magics Group's Heartscribe Program, it was thought that only a single cardioglyph could be placed permanently upon a person's heart, though in reality many simultaneous cardioglyphs are possible with different imprinting methods.
The traditional method of imprinting was to brand glyphs to surface of one's heart, the cauterising effect of the searing metal reducing the likelihood of infection. Medical improvements in more modern times mean that other forms of imprinting are possible, however for each cardioglyph to take effect, it must be imprinted by different means - such as the aforementioned branding, as well as shallow incisions, acid application and even laser-marking. Attempts to imprint a new rune with an already-applied method result in that method's last rune becoming nothing more than a mundane scar.
It goes almost without saying that recipients opt for beneficial runes, however the benefit they usually provide is very minor. Because the effects of cardioglyphs last a lifetime, and they are passed on to one's children, it is considered a human rights violation to inflict a detrimental cardioglyph upon a person - hence there is an article of the Bloodwrit dealing with this.
Similar to tracing a person's ancestry through the male Y-chromosome or female mitochondrial DNA, if one has a sufficiently complete archive of a population's individual cardioglyph sets, it is possible to trace a person's ancestry based on the cardioglyphs they were born with.