The functional ability, expressed as percentage of expected oxygen uptake, measured on the tread-mill according to the Bruce protocol, was assessed in 30 patients with anteroseptal, and in 30 patients with inferior myocardial infarction (MI), 4 months after the incident. In comparison to those with inferior MI, the patients with anteroseptal localization exhibited significantly lower values of functional ability (68.37% +/- 14% versus 75.63% +/- 11%, p < 0.05), significantly higher activities of creatine kinase (CK: 894.7 +/- 441 versus 603 +/- 330 IU, p < 0.01), significantly lower left-ventricular ejection fraction (53% +/- 6.4% versus 58.7% +/- 6.3%, p < 0.01) and higher negative correlation between CK and functional ability (r -0.85 versus r -0.72). In conclusion, anteroseptal infarction is associated with a greater decrease in functional ability then the inferior one, which is partly due to more extensive necrosis with greater deterioration in left ventricular contratility; the mere site of infarction is probably also a contributing factor.