Non-invasive methods for cardiac output measurement have been the cornerstone of studying maternal cardiac physiology in normal and pathological pregnancies in the last 20 years, since the introduction of Doppler echocardiography, around 1985 4. Echocardiographic techniques aim to estimate the SV, which can then be multiplied by the HR to obtain a CO value. This can be done using 2D, 3D or Doppler echocardiography 5. The obvious advantage is that no vascular access or calibration is needed, but an experienced operator is required, making routine use difficult.