Argon heart
A crimson-coloured gemstone obtained by defeating an Argon lizard.
--Description when selecting the Argon heart in Dragon Quest VIII.
The Argon heart and Great big Argon heart are both an item in Dragon Quest VIII
Story
Needing the Magic Mirror from the King Clavius of Argonia, The Hero & party agree to escort Prince Charmles to the Royal Hunting Ground so that he can go through the rites of passage to become king.
The party helps him by defeating three Argon lizards and winning each heart, though Charmles is unsatisfied at their small size, insisting that they look for a much bigger one. They eventually find and defeat a Great Argon Lizard, thus obtaining a Great big Argon heart.
Though Charmles manages to find an even bigger one being sold at a bazaar in Argonia, which he buys and presents as the result of his own work. Unknown by him, The Hero presents King Clavius with the heart obtained from the initiation.
Detail
Argon hearts are obtained through confronting, and defeating an Argon lizard. Doing so is required by any prince of the Kingdom of Argonia, as a right of passage into becoming king. It is also common for a member of the royal family to wear a ring with the heart used as the gem.
Great big Argon heart
A jumbo-sized Argon heart obtained through the party's hard work on the royal hunting ground.
--Description when selecting the Great big Argon heart in Dragon Quest VIII. A Great big Argon heart though rare are obtained through defeating a Great Argon Lizard. Other than being valued for their larger size, Great big Argon hearts are no different than average Argon hearts. Some merchants will be seen selling them.