AIM: Current pricing of commercial mechanical ventilators in low/middleincome countries (LMICs) markedly restricts their availability, and consequently a considerable number of patients with acute/chronic respiratory failure cannot be adequately treated. Our aim was to design and test an affordable and easy-to-build noninvasive bilevel pressure ventilator to allow reducing the serious shortage of ventilators in LMICs. METHODS: The ventilator was built using off-the-shelf materials available via e-commerce and was based on a high-pressure blower, two pressure transducers and an Arduino Nano controller with a digital display (total retail cost <75 US$), with construction details open source provided for free replication. The ventilator was evaluated (and compared with a commercially available device (Lumis-150, Resmed): a) in the bench using an actively breathing patient simulator mimicking a range of obstructive/restrictive disease and b) in 12 healthy volunteers wearing a high airway resistance and thoracic/abdominal bands to mimic obstructive/restrictive patients. RESULTS: The designed ventilator provided inspiratory/expiratory pressures up to 20/10 cmH2O, respectively, with no faulty triggering or cycling both in the bench test and in volunteers. Breathing difficulty score rated (1-10 scale) by the loaded breathing subjects was significantly (p<0.005) decreased from 5.45±1.68 without support to 2.83±1.66 when using the prototype ventilator, which showed no difference with the commercial device (2.80±1.48; p=1.000). CONCLUSION: The low-cost, easy-to-build non-invasive ventilator performs similarly as a high-quality commercial device, with its open-source hardware description, will allow for free replication and use in LMICs, facilitating application of this life-saving therapy to patients who otherwise could not be treated.