Coronary artery calcium (CAC) testing has gained attention as an inexpensive, reproducible, rapid and safe alternative to exclude coronary artery disease (CAD) in symptomatic patients and defer further invasive imaging tests. The large, single-centre study, published by Pedersen and colleagues,1 demonstrated the current utility and predictive power of a CAC score of zero. Coronary artery calcification is exclusively found in the atherosclerotic plaque, and is a marker of total plaque burden, with high scores indicative of higher totals of coronary atherosclerosis. A simple test, taking less than 1 min to acquire, without needles, injections, iodinated contrast or exercise, can determine how much atherosclerotic plaque is present in an individual. This study is the largest study of CAC in symptomatic persons done to date (11 609 patients who underwent CAC and coronary CT angiography (CCTA)). The study population included both elective (stable) and hospitalised (acute chest pain (CP)) patients. This paper demonstrated a very high sensitivity of CAC for obstructive CAD (≥50% stenosis) of 96%. More importantly, this study demonstrated a negative predictive power (negative predictive value, NPV) of 99%, providing great confidence that a person with a negative CAC (score of zero) is highly unlikely to have obstructive CAD. CAC=0 correctly excluded obstructive CAD and high-risk CAD in 99.0% and 99.6% of cases, with similar diagnostic accuracy in stable and acute CP (in-hospital) studies. In this study, among those with CAC=0, 1.8% had suspected obstructive CAD on CCTA and 1.0% had obstructive CAD and 0.4% …