Wheezing is an unusual sound made when breathing, typically when exhaling, that is high-pitched and may sound like whistling. Wheezing is a common symptom of asthma, a respiratory condition that occurs as a result of inflammation of the airways. Wheezing may also indicate other respiratory conditions and infections such as bronchitis or bronchiolitis, emphysema, COPD, and pneumonia. Wheezing may also indicate lung cancer, GERD, or heart failure, or be a side effect of smoking. In children younger than age 2, wheezing can indicate a serious viral infection. Hospitalization is sometimes required to treat wheezing when breathing is difficult and oxygen is needed.