Evolutionary tracks of 20 (dashed lines) and 25 M_⊙ (solid lines) models until central helium exhaustion computed with the Ledoux (red lines) and the Schwarzschild (black lines) criteria for the occurrence of convection for an initial composition of (X, Z)=(0.72, 0.014). The magenta line corresponds to the Ledoux 20 M_⊙ model computed with an enhanced mass-loss rate (twice our standard rates). Top panel: HR diagram, middle and bottom panels: changes in mass and in the central helium abundance, Y_c, respectively, as a function of T_eff. Radial pulsations are excited along the thick-line parts.