To any countable directed graph one can associate a C*-algebra. A natural question is then: Which graphs give rise to stably isomorphic C*-algebras? I will give an answer in a special case. I will focus on amplified graph, that is graphs with the property that if there is an edge between two vertices, then there are infinitely many such edges. Given an amplified graph G one can consider its transitive closure: A graph with the same vertex set and the property that if there is a path from u to v in G, then there are infinitely many edges from u to v in the transitive closure of G. It turns out that the C*-algebra of an amplified graph is stably isomorphic to that of its transitive closure. And that two transitively closed graphs are isomorphic if and only if their C*-algebras have the same filtrated K-theory. Thus the C*-algebras of amplified graphs are classified by K-theory, and given two concrete amplified graphs we can `see' if they give rise to stably isomorphic C*-algebras.