Boston Scientific Corp., the second- biggest U.S. heart device-maker, fell the most in five months after sinking demand for stents and defibrillators led to a fourth consecutive quarterly sales drop.

Boston Scientific declined 5.3 percent to $5.05 at 10:50 a.m. New York time, after earlier dropping to $5.02 in the biggest intraday decrease since February 2. The stock had decreased 25 percent in the past 12 months through Wednesday.

Second-quarter sales declined 7.4 percent to $1.83 billion, as revenue dropped from drug-coated stents, used to prop open clogged heart arteries, and from defibrillators used to shock a stopped heart back into a normal rhythm, Boston Scientific said Thursday. Analysts had estimated $1.88 billion. The falling revenue contributed to the Natick-based company reducing the top end of its 2012 profit forecast

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“Cardiac rhythm management and stent sales fell short of both guidance and consensus,” said Michael Weinstein, an analyst at JP Morgan in New York, in a note to clients today. “Boston’s cardiac rhythm management franchise continues to struggle,” while the stent business may be losing significant market share to Medtronic Inc.’s recently approved Resolute drug-coated stent, he said.

Earnings excluding one-time items will be 62 to 68 cents a share for the year, Boston Scientific said. The company in April forecast 60 to 70 cents. Sales may be $7.2 billion to $7.4 billion for 2012, compared with an April outlook of $7.35 billion to $7.65 billion.

Defibrillator sales dropped 9.7 percent to $355 million in the second quarter from a year earlier, while revenue from drug- coated stents fell 21 percent to $318 million, the company said.