Techniques are provided for detecting natural electrical coherence within the heart and for administering or adjusting therapy based upon whether natural electrical coherence is detected. In one example, an implantable cardioverter defibrillator (ICD), upon detecting atrial fibrillation, delays administering an atrial defibrillation pulse until a period of natural electrical coherence is detected between the left and the right atria of the heart. The ICD may further delay the pulse until the ventricles of the heart are refractory so as to help prevent triggering ventricular fibrillation. The pulses are administered at a time selected based upon the period of electrical coherence to reduce the amount of electrical energy required within the pulse to reliably defibrillate the heart. Other types of therapy besides defibrillation therapy such as anti-tachycardia pacing pulses may also be timed based upon detection periods of natural electrical coherence. Method and apparatus embodiments are described.