In a letter to the Food and Drug Administration, St. Jude Medical Inc. acknowledged quality-control issues with the handling of its Durata defibrillator leads and promised a series of improvements, the Wall Street Journal reports.

Federal regulators cited the Little Canada-based medical device maker last fall after an inspection of a California plant found significant safety concerns. Durata replaced a similar product called Riata, which was recalled in 2011 after the insulation wore away and exposed the wire cables.

Meanwhile, St. Jude Medical is one of only two companies selling a medical device at the heart of what could be a $2 billion market within a decade, Bloomberg reports. It’s a test that shows which patients need heart stents. St. Jude and San Diego-based Volcano Corporation have a duopoly market.