Like patients who have coronary artery disease (CAD), cardiac syndrome X patients report chest pain, often with exercise. They typically also experience pain during an exercise stress test, including bouts of chest pain that last longer than typical angina. However, this chest pain is not accompanied by any corresponding blockage in their coronary arteries, as confirmed by a cardiac catheterization. In other words, they show symptoms typical of CAD, but are not actually suffering from heart disease and are not at increased risk of heart attack or other cardiovascular conditions.

The causes and mechanisms of cardiac syndrome X are still largely unknown and can vary from patient to patient. However, researchers have identified certain patients who seem more prone to developing cardiac syndrome X. These include postmenopausal women and individuals who are younger than the typical patients with CAD. It may also be associated with psychiatric disorders, including anxiety.

Currently, there are several leading theories that attempt to explain the causes of cardiac syndrome X. It is important to note, however, that data on all of these possible causes is conflicted. At this time, the underlying causes Cardiac Syndrome X remain a mystery to researchers but some studies have linked it to conditions including:

• Cardiac ischemia. A lack of oxygen-rich blood flow to part of the heart. Although there are conflicting data linking ischemia to cardiac syndrome X, this theory may explain why some people suffer from chest pain without actually having heart disease. According to some studies – although not all – the ischemia may be caused by problems with tiny vessels in the heart that are so slight they do not show up on normal cardiac tests such as the electrocardiogram (EKG). This hypothesis led to the use of the term microvascular angina as an alternative to cardiac syndrome X. Other nontraditional causes of cardiac ischemia may be spasm in the coronary arteries or abnormal constriction of the blood vessels due to high levels of a natural vasoconstrictor (endothelin). Physicians may be able to assess this type of ischemia with a relatively new imaging technique, myocardial-perfusion cardiovascular magnetic resonance imaging.
  
  
• Abnormal pain perception. Another leading theory to explain cardiac syndrome X is enhanced pain sensitivity. In certain patients, cardiac pain is reported during procedures or situations that do not cause cardiac pain in healthy people. This might include exercise, or even the movement of a catheter in the right atrium or right ventricle, which should not cause ischemia or chest pain. Despite the pain, many patients do not show any other signs of heart disease, such as abnormal motions in the heart wall, a decline in function of the left ventricle or decreased blood flow to the heart.
  
  
• Ischemia plus abnormal pain perception. Still other studies have suggested that cardiac syndrome X may be caused by a combination of the two previous conditions.
  
  
• Autonomic system imbalance. The autonomic nervous system regulates all involuntary bodily functions, such as heart rate, sweating and digestion. It is divided into the sympathetic nervous system, which prepares the body for action, and the parasympathetic nervous system, which calms the body after a stress response. When functioning normally, the two systems are in balance. Cardiac syndrome X patients, however, often have an increased sympathetic drive, causing their bodies to be in “high gear” for prolonged periods of time. The precise reason for this and its connection to cardiac syndrome X is not known.
  
  
• Metabolic syndrome. The link, if any, between cardiac syndrome X and metabolic syndrome (formerly known as metabolic syndrome X) is not yet known. One component of metabolic syndrome is insulin resistance, which has been found in some patients with cardiac syndrome X and other heart diseases.
  
  
• Estrogen deficiency. For females, cardiac syndrome X could be linked to lower than normal estrogen levels in the body. This theory is partly due to the relationship between a lack of estrogen and abnormal levels of endothelin in the body. In addition, a significant number of patients with cardiac syndrome X are menopausal or post-menopausal women, who experience significant drops in estrogen levels. In addition, the exposure of women’s blood vessels to varying hormonal levels may increase the chances of microvascular changes in their vessels or arteries.