<unk>  is a cardiovascular phenomenon, in which two heartbeats occur close to each other followed by a long pause.  The second pulse is weaker than the first, and it is caused by premature contractions after every other beat, usually of the ventricles.
Pulsus bigeminus
Pulsus alternans
Pulsus paradoxus
Muffled heart sounds
Pulsus parvus et tardus
Binaural beats
Irregular pulse
Collapsing pulse