Well, in a few words, years ago I'd never think there was such a thing. A breed of love that doesn't involve lust. A breed of passion that's purer than anything imaginable. A breed of loving that originates from the core of the heart.
The picture is just a really pathetic expression of the real feeling. Sadly, it can't be described unless you've felt its divinity yourself. Things that come close don't really count, it's just gotta be it.
And, of course, the second reason I named the picture this way is because it sounds a lot like its most opposite "hardcore", a word usually used to describe the level of sickness in porn. Well, heartcore is exactly on the other side, even beyond. It's the real deal.
Oh, and though the Surreal category involves "Dream-like paintings not modeled from reality", this one is dream-like, but yet based on a true story.
You've got a right feeling. This was based on a real event,and it was indeed just the way you describe the picture. Serene,and it seems the whole world starts spinning differently just so they can stay together...