We make explicit the geometric content of Mel'nikov's method for detecting
heteroclinic points between transversally hyperbolic periodic orbits. After
developing the general theory of intersections for pairs of family of
Lagrangian submanifolds constrained to live in an auxiliary family of
submanifolds, we explain how the heteroclinic orbits are detected by the zeros
of the Mel'nikov 1 -form. This 1 -form admits an integral expression, which is
non-convergent in general. Finally, we discuss different solutions to this
convergence problem.