activities. Applying bipolar electrode in esophageal position of maximal left atrial deflection and using Butterworth high-pass filtering, the LAE provides an additional “left atrial marker channel”. By this way, atrial activities can easily be recognized even if they are superimposed by the QRS complex. Thus, LAE recording can be utilized, for example, to quickly differentiate tachycardias and extrasystolies. Esophageal left atrial electrogram recording to detect supra-ventricular tachycardias using the ICS3000 programmer (BIOTRONIK GmbH, Berlin, Germany). Approximation of the individually optimal resting AV delay for VDD pacing The lower tracking rate is programmed to a value below the sinus rate to achieve atrial controlled ventricular pacing. Then the AV delay is preset to an arbitrary value, but, for practical reasons, the use of a standard value (e. g. 150 ms) in all cases and in both modes is recommended. The rate adaptation of the AV delay has to be disabled. Now approximation of the optimal AV delay is accomplished in two steps: 1. With the preset AV delay, the interval between the left atrial deflection (LA) in the filtered esophageal left atrial electrogram (LAE) and the ventricular stimulus (Vp) is measured. 2. Then the preset AV delay (in this case 150 ms) is corrected by the amount the measured LA-Vp interval is deviating from the target value (70 ms in AV block and 50 ms in congestive heart failure patients, respectively). The resulting AV delay (prolonged if LA-Vp is shorter, shortened if LA-Vp is longer than the target value) is the approximately optimal AV interval for atrial sensing. After programming this optimal AV delay, the best possible approximation of the interval LA-Vp to the target value can be checked in the LAE. After programming this optimal AV delay, the best possible approximation of the interval LA-Vp to the target value can be checked in the LAE. Approximation of the individually optimal resting AV delay for DDD pacing The lower tracking rate is programmed to a value about 10 bpm above the sinus rate to achieve AV sequential pacing. Then the AV delay for atrial pacing remains programmed to the chosen arbitrary value of 150 ms and the rate adaptation of the AV delay remains disabled. Now approximation of the optimal AV delay takes place as in DDD pacing: 1. With the preset AV delay the interval between the left atrial deflection (LA) in the filtered esophageal left atrial electrogram (LAE), and