Raziel found the spear in the library of Vorador's Mansion in Find Vorador, with finding the three spears being a main objective to Raziel in that chapter.
After completing the puzzle in the great hall and activating several orbs, the Heart Seeker appeared in the hands of an Ancient Vampire statue in the Great Hall.
Raziel would take the spear to the Water Forge room where he would use it to imaple one of the stone Hylden statues seen above the water forge warp. This cracked the murals featuring the same spear and enabled Raziel to access further into the Mansion. When all three spears were collected and used to impale the Hylden statues, a warp to the Water Forge was created.
Several murals in Vorador's Mansion depict the spear in use - presumably showing scenes from the Ancient War, the spears are used as weapons to impale several Hylden enemies. Copying these actions on the stone Hylden statues in the water forge room enabled Raziel to solve the puzzle of the water forge room and enter the water forge.
Another image in Vorador's mansion further links the three 'ancient' spears to the Water Forge; a large stained glass windows depicts an ancient vampire wielding the Heart seeker spear with an emblem of the Water Reaver on his clothes. Vampires vulnerability to water makes this an unusual association.
The Heart Seeker as it initially appears in Defiance
close-up view of Raziel wielding the Heart Seeker spear about to impale the Hylden Gargoyle.