This is a prospective, single-arm, multi-center study to evaluate the safety and performance of the OAS in treating de novo, severely calcified coronary lesions in adult subjects. Study is going to enroll up to 429 subjects in up to 50 U.S. study sites. The primary safety endpoint is 30-day MACE and primary efficacy endpoint is procedural success. All subjects will be treated with the orbital atherectomy system and adjunctive stent. All subjects will be followed in clinic at 30 days. Additionally, all subjects will have an annual phone call or clinical follow up at each anniversary until study is closed.