NHLBI’s health topics provide information to help you learn more about heart, lung, blood, and sleep conditions, diagnostic tests, and treatments. Search Health Topics A-Z Acute Respiratory Distress Syndrome (ARDS) is a serious lung condition that causes low blood oxygen levels. Alpha-1 antitrypsin deficiency is an inherited condition in which the body does not make enough of a protein called alpha-1 antitrypsin. This raises the risk of lung diseases such as COPD. Anemia is a condition in which the blood has a lower-than-normal amount of healthy red blood cells. Angina is chest pain or discomfort that happens when an area of the heart does not get enough oxygen-rich blood. It is a common symptom of heart disease. Antiphospholipid syndrome (APS) is an autoimmune condition that causes abnormal blood clots to form in the blood vessels.

Aortic aneurysms are balloon-like bulges that occur in the aorta, which carries blood from your heart to the rest of your body. An aneurysm that bursts is a medical emergency. Aplastic anemia is a condition in which bone marrow does not make enough new blood cells for the body’s needs. An arrhythmia, or irregular heartbeat, is a problem with the rate or rhythm of your heartbeat. Your heart may beat too quickly, too slowly, or with an irregular rhythm. Clinical Trials The NHLBI leads and supports many clinical trials to help find new ways to prevent, detect, and treat heart, lung, blood, and sleep disorders. Fact Sheets and Handouts The NHLBI develops materials for patients and health professionals on many heart, lung, blood, and sleep conditions. Information from the NHLBI is based on the latest scientific findings.