A heart scan is a CT-based imaging test that takes detailed pictures of your heart and the arteries that supply it with blood. There are two main types: a coronary artery calcium scan, which measures calcium buildup in artery walls, and a coronary CT angiogram (CTA), which shows whether those arteries are actually blocked. The term “heart scan” most commonly refers to the calcium score scan, since it’s quicker, cheaper, and often marketed directly to patients.
Two Types of Heart Scan
A coronary artery calcium scan and a coronary CT angiogram both use CT technology, but they answer different questions. The calcium scan measures hardened plaque deposits in the walls of your coronary arteries and gives you a numerical score. It does not tell you whether an artery is blocked. Think of it as a gauge of how much wear and tear your arteries have accumulated over the years.
A coronary CT angiogram goes further. It uses contrast dye injected into a vein to light up the inside of your arteries, producing a detailed map of any blockages. This scan is typically ordered when a doctor already suspects coronary artery disease based on symptoms like chest pain or shortness of breath, or when other tests have come back inconclusive. It requires more preparation, involves a higher radiation dose, and is a more involved procedure overall.
What the Calcium Score Means
After a calcium scan, the radiologist calculates a number called the Agatston score. The software detects every spot of calcium in your coronary arteries and multiplies the size of each deposit by a factor based on how dense it is. All of those individual scores get added together into one total. The result falls into a general risk framework:
- 0: No detectable calcium. Your risk of a heart event in the next several years is very low.
- 1 to 99: Mild plaque buildup. Some elevated risk, but generally considered moderate.
- 100 to 399: Moderate plaque buildup. This range often tips the conversation toward starting preventive treatment like a statin.
- 400 and above: Extensive plaque. Significantly higher risk of a cardiovascular event.
Data from the Multi-Ethnic Study of Atherosclerosis (MESA), one of the largest and longest-running heart studies in the U.S., found that for every doubling of a person’s calcium score, the risk of a cardiovascular event rose by roughly 14 to 20 percent over ten years. That pattern held regardless of age, sex, or ethnicity. A score of zero, on the other hand, is genuinely reassuring and often leads doctors to hold off on medications they might otherwise recommend.
Who Should Get One
A calcium scan is not designed as a screening test for everyone. The 2019 guidelines from the American College of Cardiology and the American Heart Association recommend it primarily for people whose risk of heart disease falls in a gray zone, specifically those with an estimated 10-year risk between 5 and 20 percent. For these patients, the scan acts as a tiebreaker: a high score pushes the treatment decision one way, and a zero score pushes it the other.
Some specific situations where a calcium scan is particularly useful:
- Statin hesitancy: If you’re on the fence about starting cholesterol medication, a score of zero may mean you can safely wait and recheck in a few years.
- Older adults with few risk factors: Men aged 55 to 80 and women aged 60 to 80 who don’t have many traditional risk factors sometimes wonder if they still need preventive treatment. The scan can clarify that.
- Middle-aged adults with borderline risk: People between 40 and 55 whose calculated risk is low but who have a strong family history of early heart disease may benefit from knowing their score.
If your risk is already clearly high (you smoke, have diabetes, and high cholesterol), a calcium scan won’t change the recommendation. You already need aggressive prevention. And if your risk is very low with no concerning family history, the scan is unlikely to tell you anything you don’t already know.
What to Expect During the Procedure
A calcium score scan is one of the simplest imaging tests you can get. You lie on a table that slides into a CT scanner, electrodes are placed on your chest to track your heart rhythm, and the scan itself takes about 10 to 15 seconds of breath-holding. The entire appointment, from check-in to walking out, typically takes under 30 minutes. No contrast dye is needed, and no needles are involved.
A coronary CT angiogram requires more preparation. You’ll be asked to fast for three to four hours beforehand and avoid caffeine for 12 hours, including coffee, tea, energy drinks, and most sodas. You should still take your regular medications, especially blood pressure drugs. Because the scan needs your heart rate to be slow and steady for clear images, you may be given a beta-blocker (a heart rate-lowering medication) before the scan, sometimes as a pill and sometimes through an IV if your heart rate is still too fast. Contrast dye is injected through a vein during the scan, which can cause a brief warm, flushed feeling.
One consideration with the CTA: the contrast dye can stress the kidneys. For people with healthy kidney function (a filtration rate of 30 or above), the risk is very low. For those with significantly reduced kidney function or existing kidney disease, the dye becomes a concern and your doctor may choose a different test entirely.
Radiation Exposure
A calcium score scan delivers about 1.7 millisieverts of radiation. For comparison, a standard chest X-ray delivers about 0.1 millisieverts. So a calcium scan is roughly equivalent to 17 chest X-rays, which sounds like a lot but is still considered a low-dose scan in the world of medical imaging. A CT angiogram delivers somewhat more radiation, though modern scanners have brought the dose down considerably in recent years. For a one-time or occasional scan, the radiation risk is minimal. Repeated scans over short intervals are generally unnecessary.
Cost and Insurance Coverage
This is where things get frustrating for many patients. Medicare does not cover standalone coronary calcium scoring scans, classifying them similarly to a routine screening exam. Many private insurers follow the same policy. Out of pocket, a calcium scan typically costs between $75 and $300 depending on where you live and the facility.
A coronary CT angiogram is a different story. Medicare and most insurers cover it when ordered to evaluate suspected coronary artery disease in a patient with symptoms. If you’re having chest pain or other cardiac symptoms and your doctor orders a CTA, you’ll generally pay only your usual copay or coinsurance. The distinction matters: a calcium scan ordered for prevention is often out of pocket, while a CTA ordered for diagnosis is typically covered.
Limitations Worth Knowing
A calcium score captures only hardened, calcified plaque. Soft plaque, the kind that hasn’t yet turned to calcium and is actually more likely to rupture and cause a heart attack, doesn’t show up. This means a score of zero doesn’t guarantee completely clean arteries. It does, however, indicate that significant plaque buildup is very unlikely at that point in time.
The score also doesn’t tell you where blockages are or how severe they might be. Two people with a score of 200 could have very different situations: one might have calcium spread across several arteries with no significant narrowing, while the other could have it concentrated in a single critical spot. If the score is high enough to raise concern, a CT angiogram or stress test is usually the next step to get more specific answers.
Finally, the calcium score is a snapshot. Calcium in your arteries doesn’t go away, so your score will never decrease. What can change is how fast it progresses. Lifestyle changes and medications like statins slow the rate of new buildup, even though the number on a repeat scan may look higher simply because time has passed.