Echocardiography (Echo) is the best non-invasive technique to study aortic regurgitation (AR). The authors (AA) start reviewing the place of M-Mode (MM) and two-dimensional (2D) Echo on the identification of AR and its cause, as well as on the assessment of left ventricular function. Secondly, the AA study the role of Doppler (Dp) techniques--pulsed (PDp), continuous (CDp) and colour coded (CCDp)--analysing their relative advantages and complementarity. They conclude that AR is best identified by PDp and MM Echo, its cause may be recognized by MM and 2D Echo, and its importance is correctly judged by CDp and CCDp Echo. Left ventricular function is best appreciated by 2D Echo, helped by CDp and CCDp Echo. The AA also state that, in AR, an haemodynamic study is injustifiable, unless Echo is technically incomplete, there is pluri-valvular disease insufficiently clarified, or coronarography is necessary.