A search is performed for the production of heavy resonances decaying into top-antitop quark pairs in proton-proton collisions at √s=8  TeV. Data used for the analyses were collected with the CMS detector and correspond to an integrated luminosity of 19.7  fb−1. The search is performed using events with three different final states, defined by the number of leptons (electrons and muons) from the t¯t→WbWb decay. The analyses are optimized ...