Currently, most patients admitted to hospital with a presumed heart attack (acute coronary syndrome) remain in hospital until an invasive test can be done involving a tube and dye being inserted into the heart’s arteries (a coronary angiogram). This is to detect any life-threatening blockages that may require urgent treatment with stents or bypass surgery. Many patients have only mild blockages and are best treated with tablets and lifestyle changes alone. Modern CT scanners provide an alternative, safer, non-invasive approach to more quickly image the heart arteries. CT heart angiograms have already been applied in the outpatient setting in patients with heart pains (stable angina) and shown to improve outcomes compared with standard care. We propose to test if the use of CT heart angiograms can safely reduce the need for invasive angiography among heart attack patients who would otherwise need to undergo the risks of a traditional heart angiogram.