The key, said researcher David Holmes Jr., is using kidney-safe dyes and checking the patient's kidney function before the procedures begin.

Holmes explained that doctors normally have had to wait a few days after an angiogram to perform surgery because the X-ray contrast agent used in angiograms can be highly toxic to the kidneys and can cause problems in patients with impaired renal function that peak within three to five days.

But the Mayo researchers found that, by using different contrast agents, minimizing the amount of dye involved and carefully screening patients at risk for kidney disease, they could safely perform both procedures on the same day.

Coronary angiography is recommended before a patient's surgery to bypass blocked arteries or replace weakened valves is performed.

Since nearly 48,000 heart-valve replacements or repairs are performed every year, the study authors said the combined technique could be easier on patients.

The study is published in the current issue of Mayo Clinic Proceedings.