Murmurs arise from turbulent flow in the heart or great vessels. This may occur because of a structural abnormality of the heart, or increased flow across normal cardiac structures (e.g. innocent flow murmur in pregnancy; the tricuspid flow murmur which may be heard in atrial septal defects with a large left-to-right shunt). Turbulence occurs when laminar blood flow is disrupted. Murmurs are classified by their timing in relation to the cardiac cycle as systolic, diastolic, or continuous. Systolic murmurs are heard in up to 50% of adults. More than 90% of young adults and around 50% of older adults with a systolic murmur have a structurally normal heart on echocardiography (i.e. an innocent murmur). Diastolic or continuous murmurs always indicate structural disease. Anaemia, pregnancy, and thyrotoxicosis may result in a high-output state with a functional (flow) murmur. This chapter describes the clinical approach to the patient with a murmur.
