This paper presents a bladder model including detrusor and sphincter dynamics. The model focuses on artificially controlled bladder contractions under Electrical Stimulation. We developed a smooth muscle model linked to a geometrical description of the bladder. In order to illustrate the model performances, we simulate a well known example: the behavior of the bladder under electrical stimulation using a Brindley/Finetch implant. This approach allows us to compare our qualitative results with experimental data available in the literature. Simulated outputs (pressure, volume and urine flux) show good consistency both in shape and time course. Model sensitivity to parameter errors is evaluated. We also show how duty cycle of intermittent stimulation influences the efficiency of the bladder voiding and how simulation can help to select a stimulation pattern in order to optimize voiding while maintaining a low pressure and minimizing contraction duration.