Heartsbane is the ancestral Valyrian steel sword of House Tarly. The Tarlys have held the blade for some 500 years, and it is usually displayed proudly on a mantle in an antler sword stand at their seat at Horn Hill.
The hilt is wrought in the shape of a bow and arrow, with the pommel fashioned as arrow fletching, and the crossguard forming the limbs of the bow. This reflects the sigil of House Tarly - the huntsman.
The scabbard appears to have been carved from wood with a large gnarl in the center. The wood itself is largely left uncovered and undecorated, leaving a unique pattern that evokes a matching theme of the forest, the huntsman's domain.
During the reign of Aenys Targaryen, "Savage Sam" Tarly was Lord of Horn Hill. When the Dornish Vulture King rebelled against King Aenys, Sam led the royalist forces in the Vulture Hunt to defeat him. He wielded Heartsbane, which was said to run red from point to hilt with rebel blood.
Two centuries later during Robert's Rebellion, Lord Randyll Tarly led the vanguard of House Tyrell, Tarly men-at-arms among them, as part of the royalist forces. With Heartsbane in hand, Randyll won the Battle of Ashford, against the forces of Robert Baratheon, the future king's only military defeat.
While dining with his banished son Samwell, Randyll discovers that his partner Gilly is a wildling. Furious, Randyll points out Heartsbane, briefly explaining its history and stating that it will never go to Samwell.
Later that night, Samwell steals Heartsbane as he leaves Horn Hill with Gilly and her baby, intending to use the sword in his studies about Valyrian steel in the Citadel. It is among his effects when they arrive at the Citadel of the Maesters, heavily wrapped. After the death of his father and brother the sword would go to Samwell rightfully.
In the books
In the A Song of Ice and Fire novels, Heartsbane has been in the possession of House Tarly for five hundred years. Like Ice, it is a two-handed greatsword. It is currently wielded by Lord Randyll Tarly and, like the lands and titles of House Tarly, will pass to Dickon Tarly after Randyll passes away.