Assalamu alaykum,
This is a complex topic tbh, inshaAllah I'll try to outline it as much as I can - feel free to ask any further questions if you want.
Psychopathy affects about one-percent of the population. One thing I'd like to mention is that people with this are not exactly 'psycho' or 'insane', because, as if shown by the fact you are asking us these questions, you can tell the difference between right and wrong, what is good and bad. It is just there is this 'indifference' in their personality, they feel a lack of remorse or guilt, and can easily lie or manipulate people, or have very shallow feelings - kind of like a suppressed conscience.
I understand you don't want to go into the details of Islamic law on this issue - but if you are not capable of making the correct decisions for yourself, or say this personality disorder affects your thoughts and feelings to a great extent, you would be given leniency and the issue of accountability would be different for you. Make dua that Allah SWT makes it easy for you and also seek professional help.
And no, you don't have a black heart. Allah SWT gives us illnesses, whether physical or mental, as a trial and expiation of sins. We have been created just to worship Him, you have been created just to worship Him, that is the reason why we all exist, and it is no different for you, and being psychopathic doesn't put you at a disadvantage or means you are any less beloved to Him.
That you are concerned about the state of your heat (as we all should be anyway) is very positive and means it is still pure, and wishes to please Allah SWT, and continue to purify by doing all your acts of worship and make constant dua. And remember you may not feel remorse, but you are still highly functional, and no one is punished for having thoughts as long as we don't put them into action - in fact you would gain a lot of reward for ignoring them and having control over your nafs

, I would call this a test from Allah SWT, and remember He doesn't burden a soul with more than it can bear, that is His promise.