Gut microbiota dysbiosis has been implicated in atherogenesis and the systemic inflammatory pathways underlying acute coronary syndromes (ACS). Synbiotics, which combine prebiotic substrates with live probiotic microorganisms, may provide complementary microbiota-modulating effects. However, their role in coronary artery disease (CAD), particularly after ACS, remains unclear. We conducted a scoping review of PubMed, Ovid, Cochrane Library, ScienceDirect, Embase and Web of Science from inception to September 2026. Eligible studies were peer-reviewed human studies evaluating probiotic, prebiotic or synbiotic supplementation in acute and stable CAD. Preclinical studies and studies limited to anthropometric, lipid or glucose outcomes were excluded. Ongoing registered clinical trials were also screened. Among 2085 records, six studies met the inclusion criteria: three randomized controlled trials, one non-randomized controlled intervention study, one before-after study and one cross-sectional study. Importantly, no study enrolled patients with ACS. Randomized trials reported improvements in inflammatory biomarkers, angina symptoms and endothelial function. Two synbiotic interventions reduced circulating lipopolysaccharide and inflammatory cytokines, with improved nitric oxide bioavailability in one study. No study assessed major adverse cardiovascular events, recurrent ACS or mortality as pre-specified endpoints. Screening of ongoing trials identified only one registered randomized trial specifically investigating synbiotic supplementation after ACS. This review identified a specific evidence gap: despite mechanistic and biomarker evidence supporting microbiota modulation in stable CAD, its role after ACS remains largely unstudied. Our group is conducting SYMBIO-ACS, a randomized pilot trial of synbiotic supplementation after ACS ( NCT07411287 ), to generate initial mechanistic and clinical evidence.