Two papers in this issue demonstrate clinical consequences from the presence of clinically silent mitral regurgitation in paediatric and adolescent populations. Both are potentially important as the development of progressive doxorubicin cardiomyopathy1 and the presence of rheumatic carditis2 have long term implications. A parallel example, which highlights some of the problems inherent in attempting to derive clinical conclusions from the presence of mild regurgitation in an adult population, exists in the recent “phen/fen” controversy.3 Attempting to extract useful prognostic information from the presence of clinically silent, Doppler detected, mitral regurgitation through morphologically normal valves is not new—its negative impact on the prognosis of acute infarction has been recognised for over a decade.4 However, a fundamental prerequisite in attempting to utilise this type of information is an appreciation of the factors which underlie the presence of the colour flow signal. The appearance of mitral regurgitation is dependent upon the mechanical substrate for regurgitation itself, the fluid dynamics of the resultant flow disturbance, and lastly, processing using a colour flow mapping algorithm to produce an image. In particular, we need to question the reproducibility of findings obtained by different examiners and between different echo system implementations of colour flow mapping before we can feel comfortable about extrapolating these findings into clinical practice.