it is concluded that ( a ) electrical alternans associated with pericardial effusion is strongly suggestive of impending or established cardiac tamponade , and ( b ) electrical alternans is produced when the heart is oscillating within the pericardial sac distended by fluid with a frequency equal to one-half ( exact alternans ) , one-third ( 2 : 1 alternans ) , and one-quarter ( 3 : 1 alternans ) of the heart rate .
C0007177
cardiac tamponade
C0018787
heart