There exist several approximate criteria to locate the Frenkel line on the pressure-temperature plane. One of these criteria is based on the velocity autocorrelation function (vacf): below the Frenkel line, the vacf demonstrates oscillatory behaviour, while above it, the vacf monotonically decays to zero. The second criterion is based on the fact that at moderate temperatures, liquids can sustain transverse excitations, which disappear upon heating. One further criterion is based on isochoric heat capacity measurements. The isochoric heat capacity per particle of a monatomic liquid near the melting line is close to 3 k B (where k B is the Boltzmann constant). The contribution to the heat capacity due to the potential part of transverse excitations is 1 k B . Therefore, at the Frenkel line, where transverse excitations vanish, the isochoric heat capacity per particle should be c V = 2 k B , a direct prediction from the phonon theory of liquid thermodynamics.