ventricular fusion beat

n.
  1. A fusion beat that occurs when the ventricles are activated partly by the descending sinus or atrioventricular nodal impulse and partly by an ectopic ventricular impulse.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.