The Sacrificial Heart is just one of the many random items you'll have to find a use for in . Just like the , you need to bring this grisly trophy to a certain location if you want to claim its bounty—which is well worth it considering you'll get two passive skill points for your trouble. 

If you don't use the Sacrificial Heart and complete act three, opening the portal to act one (cruel), this can get a little confusing, since you can only travel to the necessary location by finding a waypoint once you progress a ways through the act. So, here's how to use the Sacrificial Heart, and what to do if you unwittingly travelled to act one (cruel) before using it.

How to use the Sacrificial Heart

You get the Sacrificial Heart by defeating enemies in Utzaal in act three, but it's not clear what you do with it. You need to take the heart to the Sacrificial Dais in Aggorat. This area is immediately after Utzaal, once you defeat the Viper Napuatzi boss. Progress through the city until you arrive at the Trial of Sacrifice section, then explore that area until you find a checkpoint and the Sacrificial Dais just after it. It'll be labelled as Blood Sacrifice on the map. 

If you find yourself at the entrance to The Black Chambers, you've gone too far. Approach the altar, grab the Sacrificial Dagger, interact with the altar to place the heart, and stab it to immediately get two passive skill points and two .

What if I've already progressed to act one (cruel)?

One of the issues with this quest is that if you complete act three and open the portal to act one (cruel), it becomes difficult to get back to Aggorat to use the heart at the altar. The best way to reach the location is by using the h25 com เข้าสู่ระบบ​ waypoint in act one (cruel)'s Clearfell Encampment. Activate this and you should get the option to travel straight to Aggorat by selecting act three and choosing the waypoint there.