It was empirical and inductive. Understanding being alone was a problem to Heidegger. It would be a greater problem to infer a God from that understanding.
On the other hand, St. Anselm poses a generalized stand by drawing on a negative hypothesis. God is that than which nothing could be imagined as greater. Nothing can be greater than that imaginable entity. He furthermore argues that an existent God is greater than a non-existent God. From these two premises, he concludes that the greatest imaginable entity is God and that a God that exists is greater than a God that does not exist.
St. Anselm uses absurd logic, phrased in the negative. Heidegger uses everyday and tangible experience and presents it in the affirmative. St. Anselm derives everything else from that generalization of Gods existence from logic. Heidegger finds it painstaking and nearly impossible to even completely understand the concept of being.
Charlesworth, M.J., editor/trans. Proslogion Chapter II by St. Anselm. University of Notre Dame Press, June 1979
Korab-Karpowiez, W.J. Martin Heidegger. The Internet Encyclopedia of Philosophy, 2007. Retrieved on December 26, 2007 at http://www.iep.utm.edu/heidegger.htm
Kent, WH. St. Anselm. The Catholic Encyclopedia Vol I..