The objective of this prospective, multicenter, randomized, open-label trial is to evaluate the completeness of stent expansion following a strategy of lesion preparation with either a Super High-Pressure NC PTCA Balloon (OPN NC) or a Scoring PTCA Balloon (NSE Alpha) after unsuccessful lesion preparation with conventional NC balloon angioplasty in an angiographically well-defined group of patients with severely calcified coronary lesions (grade 3) undergoing coronary stent implantation (SYNERGY everolimus-eluting stent (EES)).

Inclusion Criteria:

• Age above 18 years and consentable;
• Persistent angina symptoms despite optimal medical therapy and/or evidence of inducible ischemia;
• Angiographically-proven coronary artery disease;
• De novo lesion in a native coronary artery;
• Target reference vessel diameter between 2.25 and 4.00 mm by visual estimation;
• Calcification of the target lesion as determined by angiography (grade 3);
• Unsuccessful lesion preparation (<30% reduction of baseline diameter stenosis) with conventional NC balloon angioplasty
• Written informed consent.

Exclusion Criteria:

• Myocardial infarction (within 1 week);
• Limited long-term prognosis due to other conditions;
• Target lesion is in a coronary artery bypass graft;
• Target lesion is an in-stent restenosis;
• Target lesion is aorto-ostial;
• Target vessel thrombus.