BACKGROUND: Various strategies exist for the use of cardiac catheterization in unstable angina or non-Q wave myocardial infarction. At the authors' institution, the overall volume of cardiac catheterization has increased in recent years. OBJECTIVE: To investigate whether this increased volume of cardiac catheterization was due to adoption of a more invasive approach to the management of patients with acute ischemic syndromes. DESIGN: A retrospective cohort study was conducted using detailed chart review of coronary care unit admissions during 1990/91 and 1993/94. SETTING: A university-affiliated tertiary care referral centre with facilities for cardiac catheterization. PATIENTS: One hundred patients randomly selected from among those with unstable angina, non-Q wave myocardial infarction or chest pain not yet diagnosed in each of the study years. Detailed follow-up was complete for all patients. OUTCOME MEASURE: The use of cardiac catheterization during the index admission was documented. MAIN RESULTS: There was a trend towards more frequent use of same admission cardiac catheterization in the later period (21% [CI 14% to 31%] versus 12% [CI 7% to 20%], P = 0.09). However, after controlling for baseline characteristics and in-hospital events, the year of admission did not independently predict the use of catheterization (P = 0.60). By multivariate logistic regression, recurrence of chest pain and evidence of myocardial necrosis were most closely associated with same-admission cardiac catheterization. CONCLUSIONS: Although clinical factors partially explain the increased use of catheterization over time, there may have also been shift towards a more aggressive practice style at the authors' institution. Further study is needed to address this possibility.