A method and apparatus for identifying loss of capture in a pacing device. While pacing pulses are being delivered, the device checks for emergence of a stable asynchronous underlying intrinsic rhythm in the presence of the delivered pacing pulses. The device determines that loss of capture has occurred responsive to emergence of the underlying rhythm. In response to determining that loss of capture has occurred, pacing provided by device is modified, for example by performing a threshold test and adjusting the energy levels of delivered pacing pulses in response thereto.