Abstract: The device provides anti-tachyarrhythmia therapy, such as a countershock, to an atrium needing treatment, but delays its delivery for a programmable period of time following an indication of susceptibility to ventricular tachyarrhythmia (VT). This reduces the risk of reinducing VT during a period in which the heart is abnormally metabolically vulnerable to VT, including ventricular fibrillation (VF). The delay time may be independently programmed for different indications of VT, and may be synchronized to and delayed from the R-wave. The delay time may be adjusted, such as to exceed one second, or even to exceed several hours, in order to accommodate the metabolic abnormal susceptibility of the particular patient in the wide range of patients needing treatment of atrial tachyarrhythmias.