Venous waveform

"A" wave: atrial contraction (absent in atrial fibrillation).
"C" wave: ventricular contraction (tricuspid bulges); you won't see this.
"X" descent: atrial relaxation.
"V" wave: atrial venous filling (occurs at same time of ventricular contraction).
"Y" descent: ventricular filling (tricuspid opens).