Abstract. The use of the Heston model is still challenging because it has a closed formula only when the parameters are constant [S. Heston, Rev. Financ. Stud., 6 (1993) 1. Introduction. Stochastic volatility modeling emerged in the late nineties as a way to manage the smile. In this work, we focus on the Heston model, which is a lognormal model where the square of volatility follows a Cox-Ingersoll-Ross (CIR) 1 process. The call (and put) price has a closed formula in this model thanks to a Fourier inversion of the characteristic function (see Heston [22], Lewis [27], and Lipton [29]). When the parameters are piecewise constant, one can still derive a recursive closed formula using a PDE method (see Mikhailov and Nogel [31]) or a Markov argument in combination with affine models (see Elices [16]), but formula evaluation becomes increasingly time consuming. However, for general time dependent parameters there is no analytical formula and one usually has to perform Monte Carlo simulations. This explains the interest of recent works for designing more efficient Monte Carlo simulations: see Broadie and Kaya [13] for an exact simulation and bias-free scheme based on Fourier integral inversion; see Andersen [4] based on a Gaussian moment matching method and a user friendly algorithm; see Smith [40] relying on an almost exact scheme;