 Inclusion Criteria: Patient 18 years with symptoms mandating investigation for suspected or confirmed ACS with at least one of: ECG abnormalities e.g. ST segment depression 0.5 mm; History of ischaemic heart disease where the clinician assessing patient confirms history based on patient history or available records; Troponin elevation above the 99th centile of the normal reference range or increase in high sensitivity troponin meeting European Society of Cardiology criteria for rule-in or myocardial infarction NB troponin assays will vary from site to site; local laboratory reference standards will be used. Exclusion Criteria: 1.Signs, symptoms, or investigations supporting high-risk ACS: ST elevation MI; ACS with signs or symptoms of acute heart failure or circulatory shock; Crescendo episodes of typical anginal pain; Marked or dynamic ECG changes e.g. ST depression of 3 mm; Clinical team have scheduled early invasive coronary angiography on day of trial eligibility assessment. 2. Patient inability to undergo CT: Severe renal failure serum creatinine 250 μmolL or estimated glomerular filtration rate 30 mLmin; Contrast allergy; Beta blocker intolerance if no alternative heart rate limiting agent availablesuitable or allergy; Inability to breath hold; Atrial fibrillation where mean heart rate is anticipated to be greater than 75 beats per minute after beta blockade. 3. Patient has had invasive coronary angiography or CTCA within last 2 years and the previous investigation revealed obstructive coronary artery disease, or patient had either investigation within the last 5 years and the result was normal. 4.Previous recruitment to the trial; 5.Known pregnancy or currently breast feeding; 6. Inability to consent; 7.Further investigation for ACS would not in the patients interest, due to limited life expectancy, quality of life or functional status; 8.Prisoners HEALTH TECHNOLOGIES BEING ASSESSED: Early use of 64-slice CTCA as part of routine assessment compared to standard care. 