An implantable heart monitor (100) implanted in a patient's body having electrogram (EGM) sense electrodes (26) coupled with EGM sense circuitry (112) to generate sense events (S100) and a blood pressure measurement transducer (20) disposed in a heart chamber (10) and coupled with blood pressure measurement circuitry (112) operates to assess heart failure state (S144) as a function of mechanical pulsus alternans (MPA). MPA episodes are detected (S116), and MPA characteristics of the MPA episode are used alone or as a group as a diagnostic marker of HF state. The MPA episode data set can be stored in memory (124, 128) associated with a time and date stamp. The MPA characteristics of each MPA data set in a series of MPA data sets collected over time can be compared or plotted to determine if a trend indicative of change in HF state is discernible.