The growth of austenite during continuous heating in plain low-carbon martensite is simulated extending the analytical model by Judd and Paxton to include the carbon diffusion through the matrix. It is assumed that cementite is fully precipitated at an early stage of heating so that austenite is nucleated above the eutectoid temperature either on cementite or away from it, e.g., on prior austenite grain boundary. The austenite grows fast until all cementite particles vanish and thereafter continues to grow at a gradually increasing rate with temperature. Cementite particles remain up to a higher temperature with the increase in heating rate, initial particle size of cementite and the decrease in the number of austenite nuclei. Due to slow carbon diffusivity in austenite, the cementite free of austenite tends to dissolve faster than the cementite on which austenite was nucleated except when the particle size of cementite and/or the number of austenite nuclei is small.