Abstract: An implantable medical device (IMD) selectively switches to a more hemodynamically beneficial pacing mode upon detection of ventricular dysynchrony and/or reduced hemodynamic function during delivery of pacing pulses according to a ventricular rate stabilization algorithm. For example, in some embodiments of the invention, an IMD switches from right ventricular pacing according to a ventricular rate stabilization algorithm, to biventricular pacing according to the algorithm. The biventricular pacing can be provided according to a cardiac resynchronization therapy mode, and can involve use of an intraventricular delay between delivery of pacing pulses to the respective ventricles to improve hemodynamic functioning of a heart. The IMD monitors an electrogram signal to detect ventricular dysynchrony and/or decreased hemodynamic performance of the ventricles. The IMD can detect ventricular dysynchrony based on elongated QRS complex widths.