The radiative corrections of heavy degenerate and nondegenerate electroweak multiplets do not decouple from low-energy experiments. Their effects can be parametrized in a general renormalization-scheme-independent way. For isospin-breaking ${\mathit{h}}_{\mathit{V}}$ and chiral-breaking ${\mathit{h}}_{\mathit{A}\mathit{Z}}$ and ${\mathit{h}}_{\mathit{A}\mathit{W}}$, derived from the Z and W self-energies, a global analysis of existing neutral-current and Z and W data yields -1.2${\mathit{h}}_{\mathit{V}}$0.9, -3.5${\mathit{h}}_{\mathit{A}\mathit{Z}}$1.0, -4.4${\mathit{h}}_{\mathit{A}\mathit{W}}$2.4 (90% C.L.). The expectations for future experiments are described, and the implications for the top-quark and Higgs-boson masses, new generations, supersymmetry, and technicolor are discussed.