Current heel protection devices used in the operating room do not comply with the consensus document of the European and National (North American) Pressure Ulcer Advisory Panels. A complying prototype has been tested. Prospective cohort study comparing interface pressures. While using the prototype device, the heel interface pressure is significantly [mean 0·0 mmHg, standard deviation (SD) 0·0] less than the viscose elastic gel (VEG) mat (mean 174·8 mmHg, SD 64·5), the Action(®) heel block (mean 182·3 mmHg, SD 70·8) and the theatre table (mean 193·2 mmHg, SD 57·1). At the Achilles tendon, the prototype device (mean 16·2 mmHg, SD 19·0) is significantly superior to the Oasis (mean 183·7 mmHg, SD 67·4) and Action(®) heel blocks (mean 112·3 mmHg, SD 64·7). At the lateral malleolus, the prototype device (mean 0·0, SD 0·0) is better than the Action(®) (mean 24·3 mmHg, SD 53·4) and Oasis heel blocks (mean 20·9 mmHg, SD 49·2). At the calf, the prototype (mean 53·7 mmHg, SD 23·0) imposed more pressure than all other devices tested but was not statistically significant compared with the theatre table or the VEG mat. It is possible to design a device that protects the heel, lateral malleolus and Achilles tendon without causing hyperextension of the knee and consequent popliteal vein compression, thereby complying with the above guidelines.