WASHINGTON (AP) -- U.S. marshals and FDA investigators on Tuesday began seizing heart valves and other implantable medical devices made from cow and pig tissue by a New Jersey company because of concerns about their sterility.

The seizure from Shelhigh Inc. was expected to net an estimated 1 million parts and finished products, said Food and Drug Administration spokeswoman Heidi Rebello. The FDA said it had found significant problems in the Union, N.J., company's manufacturing processes.

The federal officials seized all implantable medical devices from the company, saying the problems could compromise their safety and effectiveness, including the sterility of the implants. The products include pediatric heart valves and conduits, or tube-like devices for blood flow, as well as surgical patches, arterial grafts and annuloplasty rings used to help repair heart valves.

The seizure followed an inspection of the company by the FDA last fall. The agency also warned Shelhigh about the problems during meetings and in two warning letters, sent in 2000 and 2005. The earlier letter cited multiple reports of infections and other problems with some of Shelhigh's products.

Violations cited by the FDA on Tuesday included the manufacturing of products in a facility with a poorly constructed and poorly maintained clean room, where sterilized devices are meant to be further processed.

The company did not immediately return a telephone message left seeking comment.

The tissue-based devices are used in many surgeries, including open-heart surgery in adults, children and infants, and to repair soft tissue during neurosurgery and abdominal, pelvic and thoracic surgery, the FDA said. Critically ill patients, pediatric patients and patients with weakened immune systems may be at greatest risk from the use of these devices, it added.

The FDA recommended doctors consider using alternative devices. Also, doctors should monitor patients with a Shelhigh implant for infections and proper functioning. Patients who think they may have received a Shelhigh device during surgery should contact their doctors for more information, the FDA added.

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