BACKGROUND: Inflammatory mechanisms in heart disease are of great interest. The proinflammatory cytokine interleukin (IL) 6 has been linked to increased morbidity in unstable angina pectoris and depressed myocardial function in heart failure (HF). METHODS: We studied the relation of IL-6 levels to C-reactive protein (CRP), infarction size, left ventricular function, and HF in acute myocardial infarction (MI) and after hospital discharge in 31 consecutive patients (19 males, mean age 69+/-13 years). Blood sampling for IL-6 was performed on admittance, four times on day 1, twice on day 2, and once daily on days 3-5, and 6 and 12 weeks later. Clinical signs of HF were evaluated daily during hospitalization and after 6 and 12 weeks. Echocardiography was performed on day 3 and at 6 weeks. RESULTS: IL-6 showed a curved time course with elevated levels already on admittance (mean+/-S.D. 19.3+/-26.9 ng/l), thereafter increasing to a peak on days 1 and 2 (maximum 68.5+/-152.9 ng/l), and then declining rapidly to lower, although not normalized, levels during hospitalization and at 6 and 12 weeks. CRP showed a similar time pattern, but with a later peak and a seemingly less rapid decline in levels. Mean levels of IL-6 and CRP on days 1-5 correlated highly (r=0.794, p<0.0001). IL-6 and infarction size did not correlate. HF during hospitalization and at 6 weeks was not related to IL-6; however, patients with HF at 12 weeks had higher IL-6 levels, both at 6 and 12 weeks. Patients on ACE inhibitors or diuretics at discharge had higher IL-6 levels at 6 weeks. IL-6 during hospitalization was not related to LVF; yet, patients with depressed LVF in the hospital and at 6 weeks had higher IL-6 levels at 6 and 12 weeks. CONCLUSIONS: IL-6 in acute MI shows a curved time course and is highly correlated to CRP. It peaks on days 1 and 2 and remains elevated even after 12 weeks. Increased IL-6 levels after hospital discharge are associated with HF and depressed LVF. Whether anti-inflammatory agents will influence left ventricular dysfunction and outcome postacute MI has yet to be determined.