May 18 (Reuters) - U.S. medical device maker Boston Scientific BSX.N said on Monday it has invested $1.5 billion in privately held MiRus LLC in return for a 34% equity stake and potential access to the startup's heart-valve business.

The deal marks Boston Scientific’s re-entry into the market for balloon-expandable transcatheter aortic valve replacement (TAVR) systems, a type of device used to treat certain heart conditions, after it exited the space in May last year citing increased clinical and regulatory requirements.

• Boston Scientific said it may acquire MiRus' TAVR business for additional cash payments totaling $3 billion if certain clinical and regulatory milestones are met. MiRus would also be eligible for additional payments tied to future sales of the device.

• TAVR systems are used to treat patients with severe aortic stenosis, a narrowing of the heart's aortic valve that can restrict blood flow.

• MiRus is developing the SIEGEL valve, an experimental device that is not yet approved for commercial sale in any country.

• Cardiac devices account for a significant share of Boston Scientific’s revenue, driven by key products such as the Farapulse and Watchman systems.

• The agreement also gives Boston Scientific an option to acquire certain MiRus mitral and tricuspid valve assets for an additional payment.

• Boston Scientific said the investment is expected to have an immaterial impact on its adjusted earnings per share in 2026.