Systems and methods for monitoring and treating patients with heart failure are described. A signal receiver may receive a heart sound (HS) signal and an impedance signal sensed from the patient. A heart sound detector circuit may use at least the received impedance signal to determine a HS detection window, and detect a HS component indicative of cardiac diastolic function from the received HS signal within the HS detection window. The system may include a heart failure detector circuit that may generate a cardiac diastolic function indicator (DFI) using the detected HS component and, in certain examples, may detect worsening heart failure using the generated DFI. The system may include a therapy circuit to deliver or adjust an electrostimulation therapy based on DFI.
