The isomorphic subgraph problem is finding two disjoint subgraphs of a graph which coincide on at least k edges. Then the graph partitions into a large subgraph, its copy and a remainder. The problem resembles the NP-hard largest common subgraph problem. In [1,2] it has been shown that the isomorphic subgraph problem is NP-hard, even for restricted instances. In this paper we present a greedy heuristic for the approximation of large isomorphic subgraphs and introduce a spring algorithm which preserves isomorphic subgraphs and displays them as copies of each other. The heuristic has been tested extensively on four independent test suites. The drawing algorithm yields nice drawings which cannot be obtained by standard spring algorithms.