The assessment of intracardiac pressures and valve stenoses by echocardiography using ultrasound Doppler signals is based on the Bernoulli principle. Left atrial pressure (LAP) may be estimated using the mitral regurgitant velocity. The right ventricular systolic pressure (RVSP) may be estimated using the tricuspid regurgitant velocity. In the presence of valvular regurgitation or an intracardiac shunt, the peak velocity of that blood flow is proportional to the difference in pressure between the two cardiac chambers. It is important to understand the limitations to the application of the Bernoulli equation in clinical practice.