Women have generally worse outcomes after myocardial infarction (MI) compared to men. The reasons for these disparities are multifactorial. At the beginning is the notion—widespread in the community and health care providers—that women are at low risk for MI. This can impact on primary prevention of cardiovascular disease in women, with lower use of preventative therapies and lifestyle counselling. It can also lead to delays in presentation in the event of an acute MI, both at the patient and health care provider level. This is of particular concern in the case of ST elevation MI (STEMI), where “time is muscle”. Even after first medical contact, women with acute MI experience delays to diagnosis with less timely reperfusion and percutaneous coronary intervention (PCI). Compared to men, women are less likely to undergo invasive diagnostic testing or PCI. After being diagnosed with a STEMI, women receive less guideline-directed medical therapy and potent antiplatelets than men. The consequences of these discrepancies are significant—with higher mortality, major cardiovascular events and bleeding after MI in women compared to men. We review the sex disparities in pathophysiology, risk factors, presentation, diagnosis, treatment, and outcomes for acute MI, to answer the question: are they due to biology or bias, or both?