Perturbation Hamiltonians simplify considerably the solution of various traveltime problems of seismic body waves propagating in heterogeneous, isotropic or anisotropic, weakly dissipative media. In this paper, the special case of the perturbation Hamiltonians, herein referred to as the linear perturbation Hamiltonians, is used to compute the second-order perturbation expansion of the complex-valued traveltime and the first-order perturbation expansion of the complex-valued traveltime gradient