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Asthma is a long-term condition in which the airways become inflamed and narrowed at times. This makes it hard to breathe. 



Atherosclerosis is a condition in which a sticky substance called plaque builds up in the arteries. This causes the arteries to narrow and can reduce blood flow through the body.


Atrial Fibrillation

Atrial fibrillation, also known as A-fib or AF, is a condition in which the heart’s upper and lower chambers do not work together as they should. This can cause your heartbeat to be too fast, too slow, or irregular.



Bleeding Disorders

Bleeding disorders are rare disorders affecting the way the body makes blood clots. If you have a bleeding disorder, you may have problems with bleeding too much after an injury or surgery.


Blood Cholesterol

Cholesterol is a waxy, fat-like substance the body needs for good health but in the right amounts. Unhealthy levels of cholesterol can lead to heart and blood vessel diseases. 


Blood Clotting Disorders

Blood clotting disorders are problems with how the body makes blood clots. If you have a clotting disorder, your blood may not clot enough when you are injured, or your blood may form clots even without an injury.


Blood Tests

Blood tests help doctors check for certain diseases and conditions. They also help check how well organs such as the heart are working and whether treatments are helping. 



Bronchiectasis is caused by damage to the airways in the lungs. The damage makes it hard to clear mucus from the airways, which can lead to frequent serious lung infections.


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.