NMT Medical Inc. lowered its revenue expectations for the second quarter and full year, citing delays in expanding its footprint in Europe and South America.

The Boston-based cardiac implant maker said sales for the three-month period ended June 30 will be about $3.2 million, not the $3.8 – $4.3 million it previously forecast for the quarter.

Full-year sales could reach $15 million, also less than the up to $18 million NMT had predicted.

CEO Frank Martin said the second-quarter shortfall was due to delays in the company’s plan to roll out new distribution channels in Europe and South America.

The news could add fuel to a fire that might be smoldering behind the scenes at NMT, where Glenn Krevlin, managing partner of hedge fund Glenhill Capital Advisors, has quietly amassed a significant stake in the Boston cardiac implant maker and might be agitating for a sale of the company.