A pacing system and method for determining a heart failure condition such as left ventricular dysfunction in a patient are provided, based upon obtaining information from cardiac signals, which information is processed and examined for an indication of the onset or progression of LVD. Since LVD is generally characterized by conduction disorders and other body responses calling for different heart rates during exercise, an examination of sensed cardiac signals is utilized to obtain data reflective of an LVD condition. In one embodiment, a QT rate responsive pacemaker is utilized, wherein variations in QT interval corresponding to heart rate are detected and stored, and then periodically analyzed to detect changes of sufficient magnitude to indicate onset of LVD. In another embodiment, changes in lower natural rate at nighttime or rest are monitored and analyzed for detection for a trend indicating LVD. Other cardiac signal parameters, such as T-wave amplitude changes during exercise, and QRS duration changes, can also be processed to obtain information from which LVD can be determined. When an LVD indication is made, the system responds automatically so as to take initial steps to treat the condition. Thus, in one embodiment, the control of pacing rate is altered so as to be better responsive to patient exercise. In another embodiment, 3- or 4-chamber pacing is initiated. In yet another embodiment, drug therapy is automatically administered.