Helium is an inert gas with a density almost one-seventh of that of air. Based on its properties breathing a mixture of helium and oxygen (heliox) will lead to a reduction in resistance through narrowed airways and consequently decreases the work of breathing. Participating infants with RSV acute bronchiolitis will be supplied with heliox (ration of 21 oxygen and 79 helium) delivered through a flow nasal cannula to evaluate heliox effect in improving their oxygenation. Heliox will act as an additive therapy to improve oxygenation in patients with lower respiratory tract infection caused by respiratory Syncytial Virus (RSV) and will decrease the need for more complicated therapies.