An implantable system for ambulatory monitoring of a high-risk heart failure patient includes a first pressure sensor implantable within an abdomen of the patient for sensing and generating an output representative of a baseline intra-abdominal pressure value of the patient and for chronically sensing and generating an output representative of an intra-abdominal pressure value of the patient at periodic intervals. At least one second implantable sensor is provided for sensing and generating an output representative of a second physiological parameter of the patient. Additionally, the system includes a processor for correlating the output of the first pressure sensor and the second physiologic sensor, and for comparing differences between the baseline intra-abdominal pressure value and subsequent intra-abdominal pressure values. The processor can reside in another implantable device or in an external device/system.