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At the kinematic endpoint of zero recoil physical momenta are parallel whichleads to symmetries in the decay distributions. We implement this observationfor decays of the type $A \to (B_1 B_2) C$ by extending the helicity formalismto include an unphysical timelike polarisation. The symmetries of the helicityamplitudes are worked out for a generic dimension six Hamiltonian for a $B \toV \ell \ell$ decay type. We obtain \emph{exact} predictions for angularobservables, e.g.,for the fraction of longitudinally polarized vector mesons,$F_L = 1/3$, which may be used to guide experimental analyses. We investigatethe vicinity of the endpoint through an expansion in the three momentum of thevector meson. New physics can be searched for in the slope of the observablesnear the endpoint. Current experimental data on $B \to K^* \ell \ell$ decaysare found to be in agreement with our predictions within uncertainties.Application to other semileptonic $B$ and $D$ decays, including $B \to V \ell^+\ell^-$, $V=K^*,\phi, \rho$ and $B \to V \ell \nu$, $V=\rho,D^*$ isstraightforward. For hadronic modes of the types $B \to V p \bar p, V \Lambda\bar \Lambda, ..$ and $B \to V \pi \pi, V \pi K, .. $ endpoint relations applyas long as they are not overwhelmed by sizeable final state interactionsbetween the $V$ and the hadron pair.

(A)symmetries of weak decays at and near the kinematic endpoint