Wider coverage for expensive implanted heart devices likely will cost the U.S. Medicare program for seniors about $2 billion over five years, the program’s administrator said on Thursday.

Other estimates ranging up to several billion dollars per year “are way too high,” Mark McClellan told reporters as he announced final rules on coverage for implanted cardioverter defibrillators. A “more realistic” projection is “maybe $2 billion or so over five years,” he said.

The devices, which deliver a life-saving shock to the heart when it beats dangerously out of sync, cost about $25,000 each. Nearly 500,000 Medicare patients will be eligible for coverage of the devices under the new rules, about one-third more than were covered previously.

The move is expected to benefit defibrillator makers Guidant Corp., Medtronic Inc. and St. Jude Medical Inc.

McClellan, who heads the Centers for Medicare & Medicaid Services (CMS), said not every eligible patient would immediately want one of the implants, which is why his cost estimate was lower than some others.

Medicare, the federal health insurance plan for the elderly and disabled, also proposed expanding coverage of ultrasound stimulation for some patients with fractures that have not healed who are participating in clinical trials. An estimated 1,000 to 2,000 patients could be eligible, CMS officials said.