A computed tomography (CT) scan of the heart is an imaging method that uses x-rays to create detailed pictures of the heart and its blood vessels.

You will be asked to lie on a narrow table that slides into the center of the CT scanner. You will lie on your back with your head and feet outside the scanner on either end.

Small electrodes will be placed on your chest and connected to an electrocardiograph (ECG) machine, which records your heart’s electrical activity. You may be given medicine to slow your heart rate.

Once you are inside the scanner, the machine's x-ray beam rotates around you. (Modern "spiral" scanners can perform the exam in one continuous motion.)

Small detectors inside the scanner measure the amount of x-rays that make it through the heart. A computer takes this information and uses it to create several individual images, called slices. These images can be stored, viewed on a monitor, or printed on film. Three-dimensional models of organs can be created by stacking the individual slices together.

You must be still during the exam, because movement causes blurred images. You may be told to hold your breath for short periods of time.

The entire scan should only take about 10 minutes.

Certain exams require a special dye, called contrast, to be delivered into the body before the test starts. Contrast can highlight the heart, which creates a clearer image.

Contrast can be given through a vein (IV) in your hand or forearm. Some people have allergies to IV contrast and may need to take medications before their test in order to safely receive this substance.

If contrast is used, you may also be asked not to eat or drink anything for 4 - 6 hours before the test.

If you weigh more than 300 pounds, have your doctor contact the scanner operator before the exam. CT scanners have a weight limit. Too much weight can cause damage to the scanner's working parts.

Since x-rays have difficulty passing through metal, you will be asked to remove jewelry and wear a hospital gown during the study.

Some people may have discomfort from lying on the hard table.

Contrast given through an IV may cause a slight burning sensation, a metallic taste in the mouth, and a warm flushing of the body. These sensations are normal and usually go away within a few seconds.

CT rapidly creates detailed pictures of the heart and its arteries. The test may be used to:

• Assess your risk for heart disease by looking for the buildup of calcium plaque on the walls of the arteries that supply blood to the heart (coronary arteries)
• Find congenital heart disease
• Identify a blockage of the arteries that supply the heart
• Look for tumors of the heart

Based on the amount of plaque in the arteries, the health care provider will calculate your cardiac calcium score.

Results are considered normal if the heart and arteries being examined are normal in appearance.

If the calcium score is very low, you are unlikely to have coronary artery disease.

Abnormal results may be due to:

• Aneurysm
• Congenital heart disease
• Coronary artery disease
• Narrowing of an artery (coronary artery stenosis)
• Tumors of the heart

CT scans and other x-rays are strictly monitored and controlled to make sure they use the least amount of radiation. CT scans do create low levels of ionizing radiation, which has the potential to cause cancer and other defects. However, the risk associated with any individual scan is small. The risk increases as numerous additional studies are performed.

In some cases, a CT scan may still be done if the benefits greatly outweigh the risks. For example, it can be more risky not to have the exam, especially if your health care provider thinks you might have heart disease.

The most common type of contrast given into a vein contains iodine. If a person with an iodine allergy is given this type of contrast, nausea or vomiting, sneezing, itching, or hives may occur. Let your doctor know if you have ever had an allergic reaction to injected contrast dye.

If you absolutely must be given such contrast, your doctor may choose to treat you with antihistamines (such as Benadryl) or steroids before the test.

The kidneys help filter the iodine out of the body. Therefore, those with kidney disease or diabetes should receive plenty of fluids after the test, and be closely monitored for kidney problems. If you have diabetes or are on kidney dialysis, talk to your health care provider before the test about your risks.

Before receving the contrast, tell your health care provider if you take the diabetes medication metformin (Glucophage) because you may need to take extra precautions.

Rarely, the dye may cause a life-threatening allergic response called anaphylaxis. If you have any trouble breathing during the test, you should notify the scanner operator immediately. Scanners come with an intercom and speakers, so the operator can hear you at all times.

Achenbach S, Daniel WG. Computed tomography of the heart. In: Libby P, Bonow RO, Mann DL, Zipes DP. Braunwald’s Heart Disease: A Textbook of Cardiovascular Medicine. 8th ed. Philadelphia, Pa: Saunders Elsevier;2007:chap 18.

Huntzinger A. AHA guidelines on cardiac CT for assessing coronary artery disease. Am Fam Physician. 2008;77.