Background: Mycobacterium chimaera is a slow-growing non-tuberculous mycobacterium that is previously known to be able to colonize the heater-cooler units (HCUs). Over 120 human confirmed cases have been reported worldwide but the real magnitude seems to be critically underestimated Methods: We provide the description and the results of a longitudinal surveillance for M. chimaera we adopted since the 6 th of December 2016 and its going on to nowadays on 35 HCUs of different brands. On these devices we provided the routine disinfection as recommended by the manufacturer and, when we found a contamination in the periodical samples, we performed the deep disinfection or we sent the HCU to the home factory to provide it, as required by the manufacturer. Results In the period 01/01/2017-23/05/2022 we performed 1191 samplings on 35 HCUs, of which 16 were the 3T of LivaNova company (type 1), 2 were HCU40 and 17 were HU35 both of Maquet (type 2). Overall, 118 positivity to M. chimaera (10.3%) were identified, specifically 83 on HCU of the type 1 (21.6%) and 35 on the type 2 (4,6%). Respectively for type 1 and 2, we found positive 41,4% and 2,9% of the tests performed in pre-disinfection samples and 15,9% and 6,3% in post disinfection. Conclusions: We ask engineers to work on new solutions to produce a new generation of heater-cooler units to simplify the cleaning and disinfection procedures, to reduce the patient risks and to increase the efficiency of cryosurgery. We suggest identifying water- free technologies that can be sanitized with enzymatic detergent in order to reduce the amount of toxic components used in the routine and deep-disinfection procedures. In any case, the "zero risk" is an impossible achievement but a detailed bio- surveillance system must be adopted for a rapid identification of rare events.