Great little game, I like the graphics, I like the concept. For me when i get the end of level 4*, it just takes me off screen, but proceed to next level, end, or allow me back onto the screen. This seems like a bug. I'd be great if you could fix, so I could finish :)
***Update***
Looks like that was everything, but at least you say so. :) At 4 levels, it feels short, I'd definitely like to see more.
One thought on a feature would be explore things to do with the heartbeat meter. Right now, it's hyper-realistic, so it's hard to actually tell when it's fast or slow, only heartbeat or no heartbeat. Since your character falls over dead and usually deaths are accompanied with a jump scare, it doesn't really seem to be doing much, almost distracting once you notice it. You could scale back the look, or add in a fade effect, and use it as a sort of enemy radar. As your heart beats faster you know there's an enemy / trap nearby, even though you might not be able to see it yet. You do have a sort of "metal gear solid" tone, but I feel like it actually breaks the tension. If you could use the heartrate meter, it could beat fastest in situations like level 4 where an enemy is right on your heels chasing you, but then it could go back down to normal the further away danger gets or off screen. Potentially, you could add a really soft tone with this, almost a quiet heartbeat sync'd with the meter, that could help build the fear and tension with a more natural and subtle sound, and possibly eliminate the "warning tone" you have now.
Food for thought. Would like more levels :) Keep it up!