There is disclosed a pacemaker, a dual chamber VDD(R) or DDD(R) pacemaker, having improved features for avoiding undesired sensor-sinus competition and providing blended sensor and sinus (atrial) control. The pacemaker employs atrial hysteresis which is used during sensing of natural atrial beats in order to enable tracking the sinus signals that occur at rates below the current pacing limit; and sensor hysteresis which prevents early takeover by sensor control and, in a DDDR pacer, controls when the sensor rate controls over a sensed sinus rate and also enables dropping the pacing rate during sensor control so as to enable finding and tracking of underlying lower rate sinus signals. The sensor hysteresis function is automatically adapted by obtaining and processing scattergram data representative of the sensor rate compared to the average of the natural sinus rate, and adjusting the sensor hysteresis function to optimally match the data. The atrial hysteresis function is also automatically adjusted as a function of rate by obtaining and processing scattergram data representative of sinus jitter, i.e., the difference between the current rate of the last atrial interval and the average sinus rate. In addition, blending of sensor and sinus control is achieved by automatic adjustment of the rate response curve based on accumulated data representative of RR signals as a function of running atrial rate.