To elucidate the nature of a pseudo-Jahn-Teller (JT) distortion from planarity, ab initio MCSCF calculations with 6-31G(d) basis sets are carried out on the ground state of the titled molecules, Cycloheptatriene undergoes the pseudo-JT distortion from a planar C-2 nu to a boar C-s conformation. In heptalene, the pseudo-JT distortion takes place in two stages, the initial step being from a symmetric planar D-2h to a skew planar C-2h structure acid the subsequent step from the skew C-2h to a twisted C-2 one. In heptafulvalene, the symmetric planar D-2h structure exhibits a third-order saddle point and, hence, the pseudo-JT distortions take place from the D-2h to D-2, C-2 nu, and C-2h ones through the respective out-of-plane nuclear deformations. Besides, the twisted D-2 structure exhibits a second-order saddle point with respect to the syn- and anti-folding motions of the seven-membered rings and the structural changes take place from the D-2 to the C-2 nu and C-2h structures. A comparison of the total energy reveals that the ground state of heptafulvalene takes the anti-folded C-2h, conformation. These structural characteristics are in good agreement with the available experimental facts. Energy component analyses reveal that in these molecules the pseudo-JT distortion from planarity should lead markedly to a lowering of the electron-nuclear attraction energy and concomitantly to raising of both the interelectronic and the internuclear repulsion energy. These energetic behaviors are accounted for in terms of the electrostatic interactions and the proximity between the nuclei and electron clouds involved in the CC and CH bonds, owing to the folding of the carbon skeleton.