A method and device for delivering a therapy in response to detection of abnormal cardiac rhythms that includes delivering a first therapy during a first delivery period, substantially simultaneous with coupling of a charging circuit and an energy storage device to generate stored energy on the energy storage device. A determination is made as to whether to deliver the first therapy during a second delivery period subsequent to the first delivery period in response to the predetermined level of stored energy not being generated on the energy storage device. The device then delivers the first therapy during a third delivery period subsequent to the second delivery period in response to the first therapy not being delivered during the second delivery period and the predetermined level of stored energy not being generated on the energy storage device.