Causes of Syncope

Syncope (fainting) has many causes. Sometimes it is not serious. In other cases, syncope is a sign of a heart problem. But treatment can help.

Outline of upper body with head turned to side. Cross section of heart in chest showing heart's electrical system in right atrium and heart walls. Arteries from heart go through neck to brain.

When Syncope Is Not Serious

Your doctor may call your problem vasovagal syncope or orthostatic hypotension. These 2 types of syncope are not serious. They can be caused by:

  • Strong feelings, such as anxiety or fear. A nerve signal may briefly change your heart rate and lower your blood pressure too much.

  • Standing for too long. Standing may cause blood to pool in your legs. When this happens, your brain may not receive all the blood it needs.

  • Standing up too quickly. Your blood pressure may not adjust fast enough to changes in posture and may drop too low. Certain medications can also cause this problem.

When Heart Trouble Causes Syncope

A heart problem can decrease the amount of oxygen-rich blood that reaches the brain. Heart trouble can be serious and may even be fatal if left untreated:

  • A slow heart rate. Electrical signals tell the chambers of the heart when to pump. But the signals may be slowed or blocked (heart block) as they travel on the heart’s pathways. This can be caused by aging, scarred heart tissue, or damage from heart disease. When the heart rate slows, not enough blood is pumped.

  • A fast heart rate. Certain problems can make the heart race. For instance, after a heart attack, also known as acute myocardial infarction, or AMI, abnormal electrical signals may be created. These signals can make the heart suddenly beat very fast. The heart pumps before the chambers can fill with blood. So less blood reaches the brain and other parts of the body. Illegal drugs, certain medications, heart disease, or an inherited condition can also cause this.

  • A heart valve problem. Blood travels through the chambers of the heart as it is pumped. Heart valves open and close to help move blood in the right direction. But a valve may not open or close fully, if it’s hardened or scarred. As a result, less blood is pumped through the heart to the brain and body.