A bag-valve mask (BVM) is a medical device used to provide positive pressure ventilation to individuals who are not breathing or not breathing adequately. It consists of a self-expanding bag, a unidirectional valve, and a facial mask. The bag is squeezed to deliver air or oxygen to the patient's lungs, while the valve prevents exhaled air from returning through the bag. BVMs are commonly used in emergency situations, such as during cardiopulmonary resuscitation (CPR) or in hospitals. Proper technique is essential for effective ventilation, and it is often used by healthcare professionals, including paramedics and emergency medical technicians (EMTs).