This is physics and not english , they have applications in certain medications that help arrest the development of cancer (cobalt-60), they can also be used as tracers for diagnostic purposes
The question is "What will happen next." That is your answer.
The person narrating has committed a murder and shoved the corpse under his floorboards. As some time passes the heart beat is a glimpse into his insanity, and how he is delusional over hearing non existent sounds. He believes he hears the heart of the person he murdered under the floorboards, which is a delusion, most likely made out of paranoia. When the police come to ask about the victim, the man almost fools them until he breaks down and confesses. He expressed annoyance at the victim earlier, saying that he could not get away from their eye, I believe. He tried to solve this by killing them, but his mind would not let him do so by making up false realities.
D. "The minds and hearts of our children depend on our loving care to grow."