Pulsus Alternans: Caught in Action.

Pulsus alternans describes an arterial pulse waveform that shows alternating strong and weak beats despite a regular rhythm. Either discovered during physical examination or catheterization, pulsus alternans indicates severe left ventricular (LV) dysfunction and poor prognosis. There has been considerable debate about the underlying mechanism. We present a tracing which depicts a classic example of pulsus alternans and gives some clues about its initiation mechanism.