Postoperative atrial fibrillation (AF) is a complication occurring in 11% to 36% of patients after cardiac operations, which results in increased morbidity and hospital costs. A new electrophysiologic screening test was developed to identify those patients at risk for development of postoperative AF. The test was validated in 50 patients (43 men and 7 women) with a mean age of 59.6 +/- 1.3 years who underwent coronary artery bypass grafting with or without other cardiac surgical procedures. After aortic and venous cannulation, but before initiation of bypass, the mid-right atrium was stimulated with a bipolar probe at 25 microA for 3 seconds. Alternating current was increased by 25 microA until AF was induced or up to a maximum of 200 microA. Postoperative AF occurred in 18 patients (36%), 17 of whom had inducible AF (sensitivity = 0.94). Of the remaining 32 AF-free patients, 13 had negative tests (specificity = 0.41). Age and sex were not factors affecting inducibility, although patients who developed AF were older than those who were AF free (63.6 versus 57.3 years, p = 0.02). Length of stay in the intensive care unit was longer for those with postoperative AF than for AF-free patients (3.6 versus 1.9 days, p = 0.02). The negative predictive value of the test was 0.93, and the positive value was 0.47. These data show that this new intraoperative technique may be used to identify patients at risk for postoperative AF. Prophylactic therapy can therefore be directed to only those patients at risk for postoperative AF.