BOSTON - Boston Scientific Corp. shares fell nearly 2 percent Tuesday, a day after posting a 64 percent decline in its first-quarter profit.

The lower profit reported after the market closed on Monday reflected downturns in two key heart device markets as well as the weight of its $27 billion acquisition of Guidant Corp.

Shares of Boston Scientific fell 25 cents, or 1.6 percent, to close at $15.84 on the New York Stock Exchange.

The Natick-based medical device maker's net income for the January-March period was $120 million, or 8 cents per share, compared with a profit of $332 million, or 40 cents per share, in the same period a year ago.

The per-share profit in the latest period was hurt because the company now has 1.5 billion outstanding shares as a result of last spring's acquisition of Guidant, compared with 830 million a year ago.

Net sales rose 26 percent to $2.09 billion from $1.62 billion in the year-ago period - a result boosted in part by the addition of Guidant's implantable defibrillators and pacemakers to diversify a Boston Scientific product portfolio that had been overly dependent on heart stents to prop open coronary arteries.

That result narrowly beat the consensus estimate of analysts surveyed by Thomson Financial, who expected sales of $2.08 billion in the latest quarter.

Boston Scientific recorded an expense of $149 million, or 10 cents per share, largely from amortization costs tied to the Guidant deal. The profit was cut a further $26 million, or 2 cents per share, from other special charges, mostly from Guidant.

Excluding such one-time items in both comparable periods, Boston Scientific said its first-quarter profit was $295 million, or 20 cents per share, down from $415 million, or 50 cents per share, in the year-ago period.

First-quarter sales of Boston Scientific's Taxus drug-coated stent fell 26 percent to $468 million from $633 million a year ago. Drug-coated stent sales have fallen off amid concerns that the devices may put patients at slightly higher risk for blood clots than older bare-metal stents.

A study released in March created more trouble for stent makers by questioning whether the tiny mesh-metal devices are more effective than less-costly drug therapy at treating patients with clogged coronary arteries who don't face imminent risk of heart attack.

Taxus had accounted for about 40 percent of Boston Scientific's overall revenue before the company acquired Guidant.

Jim Tobin, Boston Scientific's president and chief executive, told analysts in a conference call that the company is going through "a rough patch" in the stent market. But he said recent erosion in the market is easing.

Sales of defibrillators and pacemakers fell about 4 percent in the first quarter to $539 million from $562 million. Sales of those devices have recently been hurt by a series of product recalls and safety warnings involving Guidant products, which helped drive Boston Scientific's stock price down about 30 percent since the deal was completed a year ago.

Despite the problems, Tobin said the company has made progress on several fronts since acquiring Guidant in improving efficiency and quality control. For example, the company said last week that regulators have lifted a warning about quality-control problems at a Minnesota plant that makes defibrillators and pacemakers, enabling Boston Scientific to resume seeking approval for new heart rhythm devices.

"Where we are today at one year is where I originally thought we'd be at two years," Tobin said.