The stallion’s heart is still raw and steaming when it is placed before Daenerys.
As part of the ancient Dothraki motherhood ritual she begins to eat the tough, stringy flesh. The Dothraki believe that the heart of the stallion will make her son strong and swift and fearless. If she chokes on the blood or retches... the omens are less favourable.
Words edited from a wikiOIAF
For related chapter art and updates find me on Facebook - https://www.facebook.com/echoesoficeandfire/
You can also follow my Blog - Echoes of Ice and Fire, a chapter by chapter analysis of the parallels and foreshadowing in George RR Martin’s A Song of Ice and Fire book series...
Chapter Art by Alexandra Miron - https://www.facebook.com/DrawingsAlexandra/?fref=ts