My first reaction was "oooh, that's interesting."
So it shows definite potential as far as I'm concerned. I do agree that the description could be tightened up a bit. For starters, although this may be a stylistic preference, I'd just go with SCP-# as the item, and not designate a number for the heart.
Upon reaching a distance of about 5 meters away from SCP-X-1, SCP-X-2 instances will cease beating, although the liquid level in SCP-X-1 will continue to rise. Blood samples taken have shown that blood from SCP-X-1 will be from the same person as the instance of SCP-x-2 it is associated with.
I'd suggest something like: "Removal of the heart from SCP-# causes progressive tachycardia ending in cessation of heartbeat when the separation reaches or exceeds 5 meters, although the volume of liquid in SCP-# continues to increase. Analysis of the liquid shows that it is human blood, indistinguishable from the blood of the individual associated with the heart."
Again, this might be a stylistic preference.