Some people experience chest pain and shortness of breath, but when they have tests, no blockages are found in their main heart arteries. The most common cause of symptoms is related to abnormalities in the small blood vessels, also known as 'small vessel angina' or Coronary Microvascular Dysfunction (CMD). Currently, the diagnosis of CMD requires additional measurements of blood flow in the heart vessel during a minimally invasive procedure known as a coronary angiogram.

CMD affects many people and can lead to repeated hospital visits and a lower quality of life, and diagnosing the condition leads to better patient outcomes. However, there are still no widely available, proven treatments for this condition and therefore several patients remain symptomatic.

This study aims to find better ways to treat CMD, especially by understanding how the heart uses energy and how this might relate to symptoms.

Inclusion Criteria:

• Angina with non-obstructive coronary arteries

Exclusion Criteria:

• Significant epicardial coronary stenoses
• Inability to carry out bike exercise
• Contra-indication to adenosine administration
• Insulin usage with frequent hypoglycaemic episodes