Shortness of breath, also known as dyspnea, can be caused by a number of medical conditions affecting the respiratory system like asthma, COPD, pneumonia, or a pulmonary embolism. Other potential causes are heart conditions which can make it difficult for the heart to pump enough oxygenated blood to the lungs. Lifestyle and environmental factors such as smoking, obesity, or air pollution may also contribute to episodes of shortness of breath.