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The aim of this study was to investigate the possible associations between lipoprotein(a) [Lp(a)] concentrations or apolipoprotein(a) isoforms and the mode of clinical presentation of coronary heart disease (CHD) (acute thrombotic event or not).A total of 131 CHD patients and 71 age- and gender-matched individuals without known CAD (free of symptoms of heart disease) were enrolled in the study. CHD patients were classified into patients with a history of an acute coronary syndrome (ACS, n = 94) and patients with stable angina (SA, n = 37). Lp(a) levels were measured with an ELISA method, whereas apolipoprotein(a) isoform analysis was performed (in all patients and 33 controls) by electrophoresis in 1.5% SDS-agarose gels followed by immunoblotting. Isoform size was expressed as the number of kringle 4 (K4) repeats.ACS patients had higher Lp(a) plasma levels [21.9 (0.8–84.1) mg/dl] and a greater proportion of elevated (≥ 30 mg/dl) Lp(a) concentrations (25.5%) compared with SA patients [9.2 (0.8–50.5) mg/dl, P < 0.01 and 10.8%, P < 0.05] and controls [8.0 (0.8–55.0) mg/dl, P < 0.01 and 11.2%, P < 0.05], while there were no differences between SA patients and controls. The median apolipoprotein(a)-isoform size was 26 K4. In 17 (10%) patients we could not detect any apolipoprotein(a) isoform bands by immunoblotting. ACS patients had a higher proportion of isoforms < 26 K4 (low molecular weight) than SA patients (56/85 vs. 12/33, P < 0.005) and controls (10/29, P < 0.005).CAD patients with a history of ACS have higher Lp(a) plasma levels and a significantly higher proportion of low molecular weight apolipoprotein(a) isoforms compared with patients with SA or to controls.