Endothelial cells (ECs) are exposed to repetitive cyclic strain (CS) in vivo by the beating heart. The aim of this study was to assess the influence of CS amplitude and/or frequency on EC proliferation and survival and to determine the role of AKT in CS-induced EC proliferation and survival. Cultured bovine aortic ECs were exposed to 10% strain at a frequency of 60 (60 cpm-10%) or 100 (100 cpm-10%) cycles/min or 15.6% strain at a frequency of 60 cycles/min (60 cpm-15.6%). AKT, glycogen synthase kinase (GSK)-3beta, BAD, and cleaved caspase-3 were activated by CS in ECs. Increasing the magnitude or frequency of strain resulted in an earlier phosphorylation of GSK-3beta, although the magnitude of phosphorylation was similar. After CS at 60 cpm-10% for 24 h, the number of nontransfected ECs was significantly increased by 8.5% (P < 0.05). We found that the number of apoptotic ECs was slightly decreased with exposure to CS. ECs transfected with kinase-dead AKT (KA179) as well as plasmids containing a point mutation in the pleckstrin homology domain of AKT (RC25) not only prevented AKT, GSK-3beta, and BAD phosphorylation but also inhibited the CS-induced increase in cell number as well as the CS-induced protection against apoptosis (both P < 0.05). The ratio of 5'-bromo-2'-deoxyuridine-positive cells was increased when ECs transfected with RC25 and KA179 as well as nontransfected ECs and ECs transfected with Lipofectamine 2000 were exposed to CS. We conclude that AKT is important in enhancing the survival of ECs exposed to CS but is not involved in EC proliferation.