Animation of a three-dimensional echocardiogram. The heart is viewed from the apex (tip), with the apical part of the ventricles removed. The mitral valve can clearly be seen to open and close. The leaflets of the tricuspid and aortic valve are not clearly visible, but the openings are. To the left are two standard two-dimensional views.
Photo credit: Kjetil Lenes (GFDL/cc-by-sa-3.0)