Observational studies, randomized controlled trials (RCTs), and meta-analyses comparing culprit artery only PCI with multivessel PCI have reported conflicting results, [11,12,14 24,27,28] likely because of differing inclu- sion criteria, study protocols, timing of multivessel PCI, statistical heterogeneity, and variable endpoints (Data Supplement). Previous clinical practice guidelines recommended against PCI of nonculprit artery stenoses at the time of primary PCI in hemodynamically stable patients with STEMI. [9,10] Planning for routine, staged PCI of non- infarct artery stenoses on the basis of the initial angio- graphic findings was not addressed in these previous guidelines, and noninfarct artery PCI was considered only in the limited context of spontaneous ischemia or high-risk findings on predischarge noninvasive testing. The earlier recommendations were based in part on safety concerns, which included increased risks for pro- cedural complications, longer procedural time, contrast nephropathy, and stent thrombosis in a prothrombotic and proinflammatory state, [9,10] and in part on the findings from many observational studies and meta- analyses of trends toward or statistically significant worse outcomes in those who underwent-multivessel primary PCI. [12 16,21 23] Four RCTs have since suggested that a strategy of multivessel PCI, either at the time of primary PCI or as a planned, staged procedure, may be beneficial and safe in selected patients with STEMI17, [18,24,27] (Data Supplement). In the PRAMI (Preventive Angio- plasty in Acute Myocardial Infarction) trial (n 465), [24] the composite primary outcome of cardiac death, nonfatal myocardial infarction (MI), or refractory an- gina occurred in 21 patients (9%) treated with multi- vessel primary PCI, compared with 53 patients (22%) treated with culprit artery only PCI (HR: 0.35; 95% 2015 ACC/AHA/SCAI Focused Update on Primary PCI 1005 Catheterization and Cardiovascular Interventions DOI 10.1002/ccd. Published on behalf of The Society for governed by the applicable Creative Commons License CI: 0.21 to 0.58; P<0.001). 