To determine if physician subspecialization influences practice style and resource utilization, we prospectively studied 292 consecutive emergency room admissions with MI under the care of noninvasive (NON, n = 213) or invasive (INV, n = 79) cardiologists and compared the use of cardiac procedures, cost, and outcome. Patient age, gender, CAD risk factors, history of angina, MI, CHF, and prior cardiac catheterization, PTCA or CABG were comparable. Presentation of MI. non-O/Q-wave MI, use of thrombolytic therapy, peak CK, and EF did not differ. Procedures, cost, and length of stay were as follows: NON INV p-value Thall Ett (%) 45 36 NS Catheterization (%) 59 67 NS CABG (all pts, %) 13 12 NS PTCA (3VD, %) 17 35 NS PTCA (1 or 2-VD, %) 39 60 < 0.05 Total hospital days 14 17 < 0.05 ICU days 31 5.4 < 0.01 Hospital costs ($) 19,400 25,500 0.01 There were no differences between groups in the incidence of postMI complications (shock, pulmonary edema, post-MI angina, VT/VF) or reversible thallium perfusion defects. Overall, 61% of patients underwent cardiac catheterization; there were an equal number of patients with 1, 2, and 3-vessel CAD in each group. Multivariate predictors of PTCA in patients with 1 or 2-vessel CAD were previous PTCA, Q-wave MI, and care by INV. In-hospital reinfarction and mortality (8.7% vs 12.7%) did not differ; during median 12-month follow-up (96% of pts), reinfarction and mortality (11.3% vs 10.3%) were similar, In this pilot study, subspecialization impacted upon the cost of care of MI and led to increased PTCA in patients with 1 or 2-vessel CAD; larger studies are needed to determine the influence of subspecialization on long-term clinical outcomes.