An at least partly implantable system for injecting a substance into a patients body, in particular a penis erection stimulation system, comprises an infusion device (11) adapted for implantation inside the patients body, at least one reservoir (R1, R2) adapted for implantation inside the patients body in fluid connection with the infusion device to supply to the infusion device a substance to be injected into the patients body, and a cooling device for keeping the content within at least one compartment of the reservoir at a temperature below 37° C. The reservoir preferably comprises at least one first compartment accommodating or adapted to accommodate a first substance and at least one second compartment accommodating or adapted to accommodate a second substance, in particular a drug for stimulating penis erection, wherein the at least one second compartment is cooled by means of the cooling device. As a penis erection stimulation system, the infusion device preferably comprises one or more infusion needles disposed within and implanted along with one or more housings adjacent the patients left and right corpora cavernosa. A pump may be implanted inside the patients body to supply the infusion needle with infusion liquid. A drive unit also adapted for implantation inside the patients body may be arranged for advancing and retracting the tip end of the infusion needle such that it penetrates the housing at least in two different penetration areas either simultaneously or in immediate time succession, thereby injecting drugs along with the infusion liquid into the patients body for stimulating penis erection.
