Systems and methods for monitoring lung edema fluid status, such as monitoring the presence or absence of pulmonary edema, in a subject using information about responsive acoustic energy echoes from a lung are described. The system comprises, among other things, an implantable device including an acoustic transducer configured to emit acoustic energy to a lung and to receive one or more responsive acoustic energy echoes from a lung. In an example, the implantable device includes a cardiac function management device having an acoustic window in a body thereof. In another example, the implantable device includes one or more subcutaneous leads. An implantable or external processor circuit is configured to receive information about the acoustic energy echoes to compute and provide a lung edema fluid status indication; such information may include an increased number or special pattern of acoustic energy echoes received or a decreased time between successively received echoes.