Blood Essence can be easily obtained by drinking blood from most creatures, but as for Greater Blood Essence you will have to do a bit more, including that Unsullied Heart.
You'll need to get four hearts for the Great Essence, but the item now appears to only be obtained by killing higher level enemies and bosses. The best you can do is use a blood altar, to find the bosses that are within their Gear Score range. We recommend that you be at least 20 years old to increase your chances of obtaining Unsullied Heart.
You can take your time increasing your team's score, so you can be prepared, when dealing with bosses or acquiring materials for your castle.
That's all you need to know about how to get Unsullied Heart in V Rising, so we hope we've been as helpful as possible, so you can get this item quickly.