The integration of technology in the medical field has greatly improved accuracy in diagnoses, thus leading to more effective treatments. Wearable and implantable medical devices offer great potential for remote patient monitoring, particularly for heart failure (HF) patients. Continuous and accurate monitoring of the patient's hemodynamics, especially pulmonary artery pressure (PAP) and cardiac output (CO), is essential for adapting treatments and reducing repeated hospital admissions. This thesis presents an implantable wireless system for remote hemodynamic monitoring, which enables direct, continuous (24/7), and simultaneous measurement of the PAP and cross-sectional area (CSA) of the artery, that is necessary to accurately calculate the CO. The implantable system is designed to minimize clinical issues by reducing its dimensions and power consumption. Techniques for designing low-power, miniature circuits and systems to measure pressure and artery diameter are presented. An energy-efficient bridge-to-digital converter (BDC) for pressure measurements is introduced and exploits duty cycling to reduce the power consumption of the piezoresistive sensor and the instrumentation amplifier (IA) in the sensor readout, while inherently cancelling the IA's offset and 1/f noise thanks to a novel spinning method. Thus, it avoids the need for complex IAs that foresee offset-reduction techniques or calibration. This novel architecture enables high resolution and ultra-low energy consumption in bridge sensor systems, representing state-of-the-art performance in energy efficiency. An innovative method is developed to directly measure the diameter and CSA of an artery. The method exploits the inductive characteristic of an implant's anchoring loops and provides a direct and accurate measurement of the artery's CSA. The anchoring loop is used for both the fixation of the implantable system in the artery and the measurement of the artery's CSA. The deformation of the loop changes its inductance, which is correlated to the artery's diameter and CSA. An oscillator-based inductive readout circuit that measures the inductance change of a nitinol anchoring loop is presented. It enables remote monitoring of the artery's CSA and improves by a factor of four the lateral resolution of echocardiography. Ultrasound (US) is the most efficient method for powering miniature implants at great depths. To meet the requirements for a small form factor, a single implantable piezoelectric transducer is used for simultaneous power and uplink data transfer. The US powering through an 8.5 cm tissue phantom provides sufficient link efficiency, enabling wireless powering with an acoustic intensity much lower than the Food and Drug Administration (FDA) safety limit. The parallel uplink data transfer, using amplitude-shift keying (ASK) modulation, achieves a high modulation index, thus providing a robust communication link. Prototype integrated circuits (ICs) are designed and implemented in a standard 180-nm CMOS technology. A biocompatible, hermetic glass packaging approach is developed to enable long-lasting and low-cost implants. The size of the glass-packaged implantable system is 3.2 mm × 2 mm × 10 mm. The challenges of powering the glass-packaged implant are discussed, and the system's performance is verified in an in vitro experimental setup that emulates the arterial blood flow.