 2. Subjects experiencing clinical symptoms considered suggestive of ischemic heart disease eg, chest pain or discomfort or symptoms considered by the investigator to represent anginal equivalents or having evidence of myocardial ischemia eg, abnormal functional study attributed to the CTO target vessel and scheduled for clinically indicated percutaneous CTO revascularization or are subjects with multi-vessel disease andor Acute Coronary Syndrome ACS that are undergoing a staged CTO PCI procedure with the intent to achieve complete revascularization. 