ECG trace showing unstable angina pectoris. This is the symptom of paroxysmal pain consequent to myocardial ischaemia, usually of distinctive character, location and radiation. It is thought to be provoked by a transient stressful situation during which the oxygen requirements of the myocardium exceed that supplied by the coronary circulation.

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Credit: ECG trace showing unstable angina pectoris. This is the symptom of paroxysmal pain consequent to myocardial ischaemia, usually of distinctive character, location and radiation. It is thought to be provoked by a transient stressful situation during which the oxygen requirements of the myocardium exceed that supplied by the coronary circulation. Wellcome Collection. Source: Wellcome Collection.