Wenckebach period

[vĕnkə-băk′, -bäKH′]
n.
  1. A sequence of cycles in the electrocardiogram ending in a dropped beat due to atrioventricular block, with the preceding cycles showing progressively lengthening P-R intervals; the P-R interval following the dropped beat is again shortened.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.