Given an observable pair of matrices (C;A) we consider the manifold of (C;A)-invariant and observable subspaces having a fixed Brunovsky- Kronecker structure. Using Arnold’s techniques we obtain the explicit form of a miniversal deformation of a marked and observable (C;A)- invariant subspace with regard to the usual equivalence relation. As an application, we obtain the dimension of the orbit and we characterize the structurally stable subspaces.