Compared to the Mokoko Seeds, which number over a thousand, the Giant's Hearts collectibles numbers at a much more reasonable 15. This means that each one is a feat to collect, however. Be prepared to spend a significant amount of time, effort, and/or resources for each Giant's Heart you find.
The Giant's Heart on Freedom Isle can be traded for, but that doesn't make it easy to get. You'll need to fork over a tidy sum of valuable currency to claim this heart for your own.
How to get the eighth Giant's Heart in Lost Ark
You can trade for the eighth Giant's Heart with Blackfang. She won't accept just plain Silver, though. She wants Gienah's Coins for it—4,000 of them, at that.
You can get Gienah's Coins by opening up reward chests that you get for completing various quests on islands. Alternatively (or if you've run out of quests), there are daily activities that you can do to potentially earn more Gienah's coins.
There are Adventure Islands that spawn every day. These islands have the potential to offer more coin chests, which you can use for more Gienah's Coins. You can see what time the islands spawn and what rewards they offer by clicking the compass icon underneath your minimap.
For help with a much more numerous type of collectible, go check out All Mokoko Seed locations on Totopia Island in Lost Ark on Pro Game Guides!