Select the best definition of Acute coronary syndrome.

A. A microcytic anaemia caused by inadequate iron availability for haemoglobin synthesis. B. Obstruction of pulmonary arteries, commonly by thrombus originating in deep veins. C. A clinical spectrum caused by acute myocardial ischaemia, including unstable angina and myocardial infarction. D. Diffuse hepatic fibrosis with regenerative nodules and altered liver architecture.