hemisystole

[hĕm′ĭ-sĭstə-lē]
n.
  1. Contraction of the left ventricle following every second atrial contraction, producing one pulse to every two heartbeats.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.