I like to put the heart in a brine for a day or so before I cut it very thinly to use in stir fries. Onions, garlic, oregano or sage and then whatever veggies you have on hand. I find that it goes quite nicely with anything that would normally call for tough beef cuts.
I like the liver in small amounts cooked in butter and lots of garlic and onions. I cook it so that it's just barely cooked through. If you go too long it gets grainy and kinda funky. Remove the liver and veggies from the pan and then use some red wine (dry) to scrape up the pan drippings and reduce that into a sauce for the liver. It's pretty good. Like I said... small amounts. A little pastured pork liver can go a long way.
You could also make terrines or patte with liver. Served cold it can be a nice treat before a meal or served on a toasted piece of bread as part of a salad.
I've tried kidneys and while I'm sure there's a way to make then=m work well, I haven't found one preparation that I like. I do have a guardian dog that happily will eat them though. Funny thing is that he only eats them once he's buried them for a few days first. never fresh. Either way, he's happy and I get to make good use of the rest of the pig.
This is my go to book for a lot of the things that I do with the meats that I raise.
Charcuterie: the craft of salt, smoking and curing.