Yeah, this is a boss track, all right! The blending of chiptune and sampled orchestra was an inspired choice! I'm not too familiar with Touhou music, so I'll just assume that you made that brilliant decision, haha. Great work on the melodies too! And that bass is juicy!
The fake-out into a key change is a classic for a reason, and that's because it works! Good job tackling the 5/4 as well. Doing that for the first time always takes some getting used to, but I think you made it sound completely natural, and not just as something added in to score some extra points, so kudos on that!
My *only* piece of critique, and mind it is a really small thing, is that the silence right before the key change (so starting at 1:56), while a fun idea, could have been executed a tad better. I like the idea of a heartbeat kick drum, especially since it ties in nicely with the title. My main problem with it is the space, and let me explain what I mean by that.
When you use certain types of instruments, especially sampled ones, their blend creates a sense of space between the sounds, like you could imagine where in the room each instrument is being played from. The staccato strings especially contribute a lot to this sense of space, since the samples have so much reverb. When you then fade those strings away, the reverb dies down exactly the same, which kinda kills the sense of space, since that's not how reverb works, and it makes the lonely kick drum sound very dry and in your face.
Let me restate though, this is a very minor complaint! And it is the only part of this entire track that I have any fault with.
Absolutely fantastic submission, and well deserved of the high scores it's seemingly already gotten. I tip my hat to you, sir Phrog!