The OPTIMAL study is a randomized, controlled, multicentre, international study. A total of 800 patients will be randomized in a 1:1 fashion to Intravascular Ultrasound (IVUS)-guided PCI versus qualitative angio(QCA)-guided Percutaneous Coronary Intervention (PCI). Patients will be consented prior to the PCI procedure and then followed up to 2 years after the index procedure for the last enrolled patient. Patients will be followed-up at 1 month (telephone contact), 12 months (outpatient clinic visit or telephone call) and yearly after (outpatient clinic visit or telephone call).

Inclusion Criteria:

1. The patient must be ≥ 18 years of age;
2. De novo lesion in an unprotected left main coronary artery (ULMCA; ostial, shaft or distal) OR ostial left anterior descending artery (LAD) or ostial circumflex (LCX), both compatible with one Medina class of LM disease; or ostial intermediate branch disease;
3. PCI is considered appropriate and feasible by the treating interventionalist;
4. Silent ischemia, stable angina, unstable angina, or non-ST segment elevation MI;
5. Able to understand and provide informed consent and comply with all study procedures, including follow-up for at least 2 years.

Note: A patient with a prior CABG with no patent bypass on the left main coronary artery (LMCA) can be included.

Exclusion Criteria:

1. Patient is a woman who is pregnant or nursing;
2. Female patient of childbearing potential, i.e. who are not surgically sterile or post-menopausal (defined as no menses for 2 years without an alternative cause);
3. IVUS is strictly required for pre-PCI lesion severity assessment
4. ST-elevation myocardial infarction, cardiogenic shock;
5. Previous history of CABG with patent graft to the LAD and/or patent graft to the LCX;
6. Prior PCI of the LM, ostial LAD or ostial LCX at any time prior to enrollment;
7. Prior PCI of any other (i.e. non-LM, non-ostial-LAD and non-ostial-LCX) coronary artery lesions within 30 days prior to enrollment;
8. Patients unable to tolerate, obtain or comply with dual antiplatelet therapy for at least 6 months in stable patients and 1 year in ACS patients;
9. Known contraindication or hypersensitivity to everolimus, platinum-chromium, or to anticoagulants.
10. Patients requiring additional surgery (cardiac or non-cardiac) within 3 months post-enrollment;
11. Non-cardiac co-morbidities with a life expectancy less than 2 years;
12. Currently participating in another trial that is not yet at its primary endpoint. The patient is not allowed to participate in another investigational device or drug study for at least 12 months after enrollment.