The heart magic notes are a quest item obtained during Ritual of the Mahjarrat. It is found in a crate in the north-western room of Zemouregal's fort. It is seen again during Dimension of Disaster/Defender of Varrock inside the castle's library.
Matters of the Heart
The soul of Arrav is more troublesome than I'd originally thought. If I move him too far from my base, I can feel him fighting against my will. I must find a way to strengthen my hold over him to subjugate him further, else it would be better to destroy him and be done with it.
I have been working on an enhancement prism, but the results with ordinary glass weren't enough - I needed a better material.
Thankfully, I believe I have found what I need in a volcano on Karamja - a rare black mineral called obsidian. I'll construct a prism from this.The prism works and my spell is enhanced! Now, I can make better use of Arrav against Varrock. In life he was its protection, in death its destroyer... an example of all the fates of 'heroes'. The prism is very fragile though, so I'll need to lock it away from those clumsy zombies.