NEW YORK (Bloomberg) ? Tyco International Ltd. and its partner Palatin Technologies Inc. warned doctors of life-threatening side effects and two deaths among patients tested with the companies? NeutroSpec radiology imaging agent.

The complications occurred within minutes of injection, and the patients died of heart failure within a half hour, the US Food and Drug Administration said on Friday in a statement. Cranbury, New Jersey-based Palatin said in a statement that the patients had severe heart conditions and were undergoing tests other than for the US approved application, which is for diagnosing appendicitis.

Some patients were resuscitated after their hearts suddenly stopped, while others developed abnormally low blood pressure or had trouble breathing, the FDA said. Trained health-care providers with access to resuscitation equipment should closely watch patients receiving NeutroSpec for at least an hour after injection, the agency said.

Palatin officials did not immediately return phone calls seeking comment. The company said in its statement that no cause-and-effect connection has been established between the imaging agent and the complications.