The diagnosis of myocardial infarction (MI) depends on a rise and/or fall of cardiac biomarkers such as troponins in the appropriate clinical context. Conventional troponin assays lack sensitivity and precision at the low serum concentrations observed in the early hours after the onset of chest pain. New, highly sensitive troponin assays may offer improved certainty in these early hours. Many of these assays can detect troponins reliably at serum concentrations that occur in patients with chronic stable heart disease and even in asymptomatic healthy individuals. Indiscriminate use of these previously undetectable concentrations for the early diagnosis of acute MI will be accompanied by reduced specificity. However, they are likely to improve risk stratification of patients with chronic heart disease. This review focuses on the available highly sensitive troponin assays and their likely use in the diagnosis of acute MI and risk stratification of patients with heart disease.