One of the coolest things I heard in Anatomy and Physiology (have not taken the time to verify this on line) was that when a two hearts get in proximity they can match their beats. As a transplanted heart gets close to the heart that it is replacing they synchronize. I may be saying this the wrong way from a medical perspective. But I trust that I have no one reading this who is a doctor. I have thought about this as a few times through our adoption of Bella.
The first time I thought of it was when Jason and I got our EKG for the medical part of our application. Coincidentally, we have the same abnormality (minor though it is). Apparently, it is not a commonly occurring abnormality and our doctor got a kick out of the fact that we both have it. Hmmmm. synchronicity.