A doctor will often ask for an angiogram if you’ve been experiencing pains in your chest or if you’ve been suffering from a severe shortness of breath. You’ll be told not to eat or drink anything from at least the night before the test, and any blood-thinning medication you’re taking would need to be stopped for several days beforehand.

Angiography is an ‘invasive procedure’, as doctors put it and, although not painful, an angiogram can be an unpleasant experience. A catheter is inserted into a blood vessel in the arm or leg under a local anaesthetic, and guided towards the heart before dye is injected into an artery. A cylindrical camera is placed over the chest and takes images from a variety of angles, with more dye being injected for each new photograph. One injection puts dye into the main pumping chamber, which can cause a warm, and sometimes unpleasant, feeling for 30 seconds or so.

The process takes up to 30 minutes, although the patient has to lie still for up to six hours after the catheters have been removed. You will need a nurse to help you stand up during this time as the desire to go to the bathroom and to expel the dye will be overwhelming.

Although doctors are now looking at less invasive procedures, such as Doppler ultrasound and magnetic resonance angiography, a standard angiogram remains the first-choice option.

This is a pity as angiography is a crude and often unreliable test. Dr Howard Wayne, of the Noninvasive Heart Center of San Diego in California, says that the main coronary arteries, monitored by an angiogram, contain only a quarter of the total coronary blood flow. And even this partial view is further reduced by the fact that an angiogram cannot assess blood vessels smaller than 0.5 mm in diameter.

In addition, an angiogram is only a snapshot in time whereas the cardiologist really needs to know how long ago there was a major change to the blood flow to a specific area of the heart.

Cardiologists are only just beginning to understand that narrowing of the coronary arteries is of minor importance when assessing heart health. When angiograms of patients with stable and unstable angina are compared, no anatomical differences are visible to separate the two different types of patient, says Dr Wayne.

This may also explain the unreliability of the test. In one study, half of the 171 patients recommended for coronary angioplasty (where arteries are widened by tiny inflatable ‘balloons’) on the basis of angiography were later found not to need surgery after all. In the end, only seven of the original group went on to have angioplasty (JAMA, 1992; 268: 2537-40).