Acute coronary syndromes (ACS) comprising acute myocardial infarction and unstable angina pectoris are prevalent causes for patient admission to hospital. Research has disclosed variations in the quality of in-hospital care of such patients as measured by levels of adherence to evidence-based management recommendations. This review aimed to identify:the patient characteristics and system of care factors which reliably predict an increased likelihood of suboptimal care; andeffective strategies for optimizing care.A systematic review was undertaken of studies that evaluated the relationship between predictor-of-quality variables (patient or hospital characteristic or quality improvement intervention [QII]) and care processes and/or outcomes.With regards to patient characteristics, increasing age and the co-existence of diabetes mellitus, renal disease, chronic obstructive lung disease, major mental health disorders, and significant co-morbidity burden were associated with underuse of effective therapies, as was the presence of congestive heart failure as a complication of ACS and the absence of chest pain as presenting symptom. Studies of sex-, race- or socioeconomically-related differences in care yielded inconsistent results.In terms of system of care factors, risk-adjusted studies suggested that there was no relationship between quality of care and the specialty of the admitting clinician (cardiologist versus non-cardiologist). However, the admission to tertiary, urban or high volume hospitals predicted higher-quality care compared with admissions to non-tertiary, rural, or low volume hospitals, while the presence or absence of on-site invasive facilities was not a reliable predictor. No consistent differences in quality were noted between managed care and fee-for-service arrangements, or between Veterans Health Administration and Medicare funding systems.The determination of effectiveness of QIIs is constrained by a paucity of rigorous evidence. The most effective interventions appear to be multifaceted, guideline-based quality improvement programs led by clinician leaders that target multiple key care processes and include repeated performance feedback. Single interventions that appear useful include clinical pathways in emergency departments and coronary care units, nurse-mediated thrombolysis protocols, clinical pharmacist-mediated academic detailing, checklist-based patient feedback to clinicians, and system re-design based on process analysis. The impact on quality of nationally released practice guidelines published by professional organizations was minimal in the absence of localized methods of implementation.Certain patient and system of care factors predispose patients to receive suboptimal care which, if known to the individual clinician, allows for greater vigilance of personal practice when he or she is confronted with such circumstances. For professional groups and health institutions, this information when combined with knowledge of effective strategies for improving care provides opportunities for optimizing both clinical care and patient outcomes.