The agency has been “investigating reports of deaths and serious cardiopulmonary reactions” in patients given ultrasounds and, as early as this week, may issue Black Box warnings since docs use the imaging agents to enhance diagnosis of heart problems, The WSJ Health Blog reports tonight. The warnings are expected to be issued for Definity, which is made by Bristol-Myers Squibb, and Optison from General Electric.

The drugs, known as contrast agents, sharpen the pictures of the heart during a procedure called echocardiography. The ultrasound exams help doctors diagnose heart defects and malfunctions. The FDA has also asked the drugmakers to update their product labeling, which they have agreed to do, the FDA spokeswoman tells the site.

The warnings will caution docs not to use the meds in patients with unstable angina, acute heart attacks and unstable cardiopulmonary disease, according to the WSJ Health Blog, and the labels will instruct docs to monitor patients’ heartbeats for trouble with an electrocardiogram, or ECG, for a half-hour after the ultrasound exam is finished. However, it’s worth noting that the imaging agents are used in only a small fraction of echocardiograms.

A Bristol-Myers spokesman confirmed the company is in discussions with the FDA about revising the instructions for use for Definity. He declined to characterize the changes being discussed and said the company “will communicate them as soon as they are final,” the Health Blog writes. Common side effects from Definity include headache, back or kidney pain and flushing. Sales of Definity were about $65 million last year.

Optison, a similar medicine, has been off the market since late 2005, when it was recalled because of manufacturing problems. A letter posted on GE’s Web site early last month said the company expected to resume selling Optison in September or October. A GE spokesman wasn’t available for comment on the FDA’s planned action.