Abstract Objective preHEAT was a randomised controlled feasibility trial to determine how best to measure skin necrosis in breast reconstruction to inform the design of a larger multicentre trial. Background Mastectomy skin flap necrosis (MSFN) is a serious complication resulting in prolonged wound healing. Local heat preconditioning of the MSF before surgery has been shown to reduce skin necrosis in immediate breast reconstruction patients (IBR). Method preHEAT was a single-centre, randomised control two-arm single-blind parallel arm feasibility trial of local heat preconditioning in breast cancer patients undergoing SSM and NSM at Guy’s and St Thomas’ Hospital, London, UK. All patients undergoing IBR above the age of 18 were included. Intervention patients heated breast skin to 43 °C in three, 30-min cycles interrupted by spontaneous cooling using hot water bottles. The primary aim was to compare measurement of skin necrosis using binary ‘yes/no’ assessment, the SKIN score, and wound area. Results One hundred forty-one patients were randomised over a 2-year period (71 heated group, 70 controls). There was near perfect agreement between assessors using the “yes/no” measurement of necrosis. The proportion of patients experiencing necrosis in controls was 35% (n = 23/66) in the heated 26% (n = 18/68]). In the control group, 17% (n = 4/23) patients experiencing necrosis required surgical intervention for necrosis compared to 11% (n = 2/18) in the heated group. Conclusion The binary outcome of MSFN “yes/no” is a suitable and reliable primary outcome measure of necrosis and was superior to the SKIN Score or necrosis area. The trial study design is feasible for a larger definitive trial. Trial registration ISRCTN15744669 . Date of registration: 25/02/2018