1. The coming together of waves in various media in such a way that the crests of one series correspond to the hollows of the other, the two thus neutralizing each other; or so that the crests of the two series correspond, thus increasing the excursions of the waves. 2. Collision within the myocardium of two waves of excitation at the junction of territories controlled by each, as is seen in atrioventricular (AV) dissociation. 3. Also in AV dissociation, the disturbance of the regular rhythm of the ventricles by a conducted impulse from the atria, by a ventricular capture (interference beat). 4. The condition in which infection of a cell by one virus prevents superinfection by another virus, or in which superinfection prevents effects that would result from infection by either virus alone, even though both viruses persist.