Its awful to imagine someone was trapped in rubble by their own heartbeat.
edit: Also, if somehow the radar had multiple heartbeats, we would have used "its heartbeats" rather than "their heartbeats."
disclaimer: I am not a grammarian or a linguist (IANAGOAL?)
(It's a valid sentence, honest)
But definitely not a sentence.
;0)>
Odd that I have -4 points on it - it seemed vaguely connected to the rest of the thread.
The grammar rules that you find written down are an approximate encoding of rules that native speakers have all internalized. These written down rules are not perfect, and have edge cases. They allow for sentences that a native speaker would not formulate or easily comprehend. The "Buffalo" sentence is an example of such an edge case.