### Abstract

We report on joint work with V. Kostrykin and J. Potthoff. On metric graphs and for a certain class of Laplace operators a representation for the heat kernel in terms of walks is given. This representation is obtained from a corresponding one for the resolvent derived previously by two of the authors. This results in a Selberg-Gutzwiller type formula for the trace and extends earlier results by other authors in the context of quantum graphs.