Most of the heuristic search based planning systems perform guided search evaluating states to compute a heuristic measure. Although recent planners are quite efficient, the time spent in computing the heuristic measure is still an issue that the community has to address. In this work we present an extension to the heuristic of the relaxed plan introduced by the FF Planner. We propose to integrate in the heuristic measure the actions preconditions difficulty, which is computed during the relaxed plan extraction phase. Results show that the number of evaluated states and the time to compute plans are decreased using this integrated heuristic.