Rotationally resolved spectra of h(2)- and d(1)-formic acid embedded in liquid helium droplets have been recorded in the spectral region of the O-H (nu(1)) and C-H (nu(2)) stretch vibrations. Accidental resonant mixing between the nu(1)-band of h(2)-formic acid and the combination bands (nu(2)+nu(7)) and (nu(2)+nu(9)) has been observed. The fundamental nu(1) band can interact via Fermi resonance with the (nu(2)+nu(7)), and the (nu(2)+nu(7)) via Coriolis coupling with the (nu(2)+nu(9)) band. Examination of the resonance induced line-broadening effects suggests that the helium environment modifies vibrational relaxation dynamics. The 2nu(3) Cdouble bondO stretch overtone is also observed and was assigned by a density functional theory (DFT) ab initio calculation. The spectroscopic constants are determined by fitting all spectra with a standard gas phase Hamiltonian.