  Tidal dissipation in binary star and planetary systems is poorly understood.
Fortunately, eccentric binaries known as heartbeat stars often exhibit tidally
excited oscillations, providing observable diagnostics of tidal circularization
mechanisms and timescales. We apply tidal theories to observations of the
heartbeat star KIC 8164262, which contains an F-type primary in a very
eccentric orbit that exhibits a prominent tidally excited oscillation. We
demonstrate that the prominent oscillation is unlikely to result from a chance
resonance between tidal forcing and a stellar oscillation mode. However, the
oscillation has a frequency and amplitude consistent with the prediction of
resonance locking, a mechanism in which coupled stellar and orbital evolution
maintain a stable resonance between tidal forcing and a stellar oscillation
mode. The resonantly excited mode produces efficient tidal dissipation
(corresponding to an effective tidal quality factor $Q \sim 5 \times 10^4$),
such that tidal orbital decay/circularization proceeds on a stellar evolution
time scale.
