Colour flow mapping (CFM) produces a two-dimensional representation of blood flow within the heart and great vessels by analysing data acquired from multiple pulsed Doppler sample volumes, and displaying mean velocity and turbulence of flow at each site. Constraints imposed by the time required to process these data mean that CFM cannot be used for precise velocity measurements. Instead it depicts flow patterns in healthy and abnormal hearts and the precise location and direction of turbulent jets. CFM is an integral part of the standard echocardiographic examination; it is especially useful in neonates and children with congenital heart disease, and in adults for the semi-quantitative assessment of valve regurgitation, and the description of flow patterns in complex acquired disease. Transoesophageal echocardiography with CFM is invaluable for the diagnosis of mitral prosthetic valve dysfunction, aortic dissection, and complications of infective endocarditis. Intraoperative epicardial CFM provides the equivalent of intraoperative angiography.