Recently it has been shown that clear reproducible Doppler signals can be recorded from the lung parenchyma by means of a pulsed Doppler ultrasound system incorporating a special signal processing package parametric Doppler, TPD, EchoSense Ltd., Haifa, Israel). These lung Doppler signals (LDS) are in full synchrony with the cardiac cycle and can be obtained from the lungs, including areas remote from the heart and main pulmonary vessels. The LDS waves typically have peak velocities of up to 30 cm/s and are of relatively high power, making it possible to detect them despite the aforementioned attenuation by the air in the lungs. The LDS are thought to represent the radial wall movement of small pulmonary blood vessels, caused by pressure pulse waves of cardiac origin which propagate throughout the lung vasculature. The LDS may contain information of significant diagnostic and physiological value regarding the pulmonary parenchyma and vasculature, as well as the cardio-vascular system in general.