Self-healing is achieved with a dual-microcapsule system utilizing epoxy-amine chemistry in a high temperature cured thermosetting epoxy polymer. One capsule contains a modified aliphatic polyamine prepared by vacuum infiltration of polyoxypropylenetriamine into hollow polymeric microcapsules. The second capsule contains a difunctional epoxide and reactive diluent. Healing efficiency is accessed through recovery of fracture toughness and excellent long-term stability at ambient conditions is demonstrated.