Objectives Bleeding is an established complication following cardiac catheterization and lower preoperative hemoglobin concentration is a potentially modifiable risk factor for adverse outcomes after cardiac surgery. However, typical changes in serum hemoglobin concentration after cardiac catheterization are poorly defined. The authors sought to identify the pattern of change in serum hemoglobin concentration within 7 days after cardiovascular catheterization, factors associated with this change and any association with adverse outcomes. Design Retrospective observational study over a 1-year period. Setting U.S. academic medical institution. Participants Participants were 284 adult patients with baseline hemoglobin concentration=12 g/dL undergoing nonemergent cardiac surgery after cardiovascular catheterization via the femoral arterial route. Interventions None. Measurements and Main Results Lowest daily hemoglobin concentration was recorded where available for up to 7 days after catheterization and before surgery. Generalized estimating equations identified the pattern of change in serum hemoglobin while regression models identified factors associated with hemoglobin decline. Following cardiovascular catheterization average serum hemoglobin declined over time, reaching a nadir 1.4 g/dL (95 CI 1.0-1.8) below baseline 6 days after catheterization. A higher baseline hemoglobin concentration and lower body mass index were associated with greater maximal decline in hemoglobin concentration after catheterization. Acute preoperative hemoglobin decline was not associated with acute kidney injury (AKI) or a composite adverse outcome that may reflect organ ischemia. Conclusions In a cohort of patients before cardiac surgery serum hemoglobin declines during the week after cardiac catheterization, with maximal average decline observed 5 to 7 days after catheterization. ? 2014 Elsevier Inc.