A pacemaker system is provided for rate responsive pacing, wherein rate is controlled as a function of two or more sensor inputs, each sensor providing a signal representing a respective different control parameter. Preferably a first sensor signal represents a physiologically accurate although slow response signal such as OT interval, and a second sensor represents a relatively fast response such as activity. The two parameter signals are processed so that they are directly comparable and can be compared as indicators of pacing rate throughout the desired pacing range. The algorithm utilizes a parameter control reference curve for each respective parameter, such reference curve representing the desired correlation between pacing rate and the parameter signal. Rate control is accomplished by determining the difference between each processed parameter signal and its corresponding reference point for the current pacing interval, and logically analyzing the two differences to determine which is used to indicate change in pacing rate. Each parameter reference curve is automatically adjustable to correspond to patient conditions. Automatic drift correction of the fast response parameter, such as activity, is used to compensate for conditions where the fast response signal is not likely to be physiologically reflective of the patient condition.