To determine if greater managed care market share is associated with greater use of recommended therapies for fee-for-service patients with acute myocardial infarction.

We examined the care of 112 900 fee-for-service Medicare beneficiaries aged ≥65 years who resided in one of 320 metropolitan statistical areas and who were admitted with an acute myocardial infarction between February 1994 through July 1995. Use of recommended medical treatments and 30-day survival were determined for areas with low (<10%), medium (10% to 30%), and high (>30%) managed care market share.

After adjustment for severity of illness, teaching status of the admission hospital, and area characteristics, areas with high levels of managed care had greater use of beta-blockers (relative risk [RR] for greater use = 1.18; 95% confidence interval [CI]: 1.06 to 1.29) and aspirin at discharge (RR = 1.05; 95% CI: 1.02 to 1.07), but less appropriate coronary angiography (RR = 0.93; 95% CI: 0.86 to 1.01) and reperfusion (RR = 0.95; 95% CI: 0.85 to 1.03) when compared with areas with low levels of managed care.

Medicare beneficiaries with fee-for-service insurance who resided in areas with high managed care activity were more likely to have received appropriate treatment with beta-blockers and aspirin, and less likely to have undergone coronary angiography following admission for myocardial infarction. Thus, the effects of managed care may not be limited to managed care enrollees.