Lipoprotein(a), or Lp(a), levels and the effect of proprotein convertase subtilisin/kexin type 9 (PCSK9) inhibition on Lp(a) during the peri-infarction and early postinfarction period are not well characterized. This study aimed to describe the trajectory of Lp(a), as well as the effect of PCSK9 inhibition on that trajectory during the peri-infarction and early postinfarction period. Lp(a) levels were obtained within 24 hours of hospital admission as well as within 24 hours of hospital discharge and at 30 days from 74 participants who presented with a NSTEMI (troponin I >5 ng/ml) or with a STEMI and were enrolled in 2 randomized, double-blind trials of evolocumab and placebo (Evolocumab in Acute Coronary Syndrome [EVACS I]; ClinicalTrials.gov, NCT03515304 and Evolocumab in Patients With STEMI [EVACS II]; ClinicalTrials.gov Identifier: NCT04082442). There was a significant increase from the pretreatment level in the placebo-treated patients, from 64 (41,187) nmol/L to 80 (47, 172) nmol/L at hospital discharge and to 82 (37, 265) at 30 days. This was primarily driven by the results from participants with high Lp(a) at hospital admission (>75 nmol/L) in whom the median increase was 28% as compared with a 10% increase in those with pretreatment Lp(a) of <75 nmol/L. In contrast, there was no significant change from the pretreatment level in the evolocumab-treated patients regardless of pretreatment Lp(a) levels. In conclusion, Lp(a) rises during the peri-infarction and early postinfarction period in patients with acute myocardial infarction. The increase was prevented by a single dose of subcutaneous evolocumab given within 24 hours of hospital admission.