Both pneumonia and heart failure are common conditions that can result in shortness of breath. By definition, pneumonia is an inflammation that results in filling of the air spaces of the lungs—usually due to infection. Heart failure can also result in congestion of the lung air spaces by salt and water displaced from the circulation because of a high fluid pressure “backed up” behind the left ventricle. On a chest x-ray, different distributions of opacification of the lungs can help distinguish the two conditions. Pneumonia is usually associated with fever. Heart failure may be associated with other findings of fluid retention including elevation of a heart failure blood test. Nevertheless, especially in patients with a history of heart disease, distinguishing between the two conditions can be difficult including the possibility that both could be present at the same time. Whereas pneumonia usually requires antibiotics to improve, heart failure with lung congestion may need therapies to increase the removal of excess salt and water from the body.