BACKGROUND Intense medical and economic pressures have created "fast track" cardiac surgery in which clinical services are streamlined and early discharge is encouraged. Does this strategy promote significant cost saving or merely cost shifting? In a global system of reimbursement, the economic benefit of decreasing patient length of stay may be offset by high rates of patient readmission. This study was undertaken to determine the 30-day readmission rate after cardiac surgery and to analyze trends of readmission diagnoses. RESULTS From October 1, 1996 to July 31, 1997, 460 consecutive cardiac surgical operations were performed at 1 institution. There were 25 deaths and 8 patients who remained as inpatients at the 30-day postoperative deadline for readmission. Two patients had 2 operations. Therefore, 527 operations were performed on 525 patients. There were 110 readmissions after 527 operations for a readmission rate of 20.9%. A significant number of readmissions (49%) were to outside hospitals. Readmission diagnoses were: atrial fibrillation (23%); angina, congestive heart failure, or ventricular tachycardia (20%); leg wound (15%); sternal wound (5%); pneumonia (5%); gastrointestinal complaints (5%); neurologic event (2%); and miscellaneous (25%). Patients discharged > or = 7 days postoperatively were twice as likely to be readmitted as those discharged on postoperative days 4, 5, or 6. CONCLUSIONS Readmission after cardiac surgery is common and frequently (49%) to outside institutions. Patients discharged > or = 7 days postoperatively represent the patients at greatest risk of readmission and, therefore, warrant closer scrutiny before discharge.