A normal central venous pressure (CVP) waveform has three upward (positive) waves marked a, c, and v and two downward (negative; descent) waves marked x and y. The a portion of the wave corresponds to atrial contraction. The c portion corresponds to ventricular contraction against a closed and bulging tricuspid valve. The v portion corresponds to the passive filling of the atria. The x portion of the wave corresponds to atrial relaxation as the tricuspid valve is pulled away from the right atrium by contracting ventricle. Lastly, the y portion of the wave corresponds to tricuspid valve opening and ventricular filling.