A heart monitoring apparatus, comprising: an ultrasound-frequency signal generator configured to drive an ultrasound transducer； a receiver configured to receive ultrasound-frequency return signals reflected from a target region in a patient's lungs and detect Doppler shifts of the return signals； and a processor configured to (a) process the detected Doppler shifts with a noise reduction algorithm and output processed power and velocity data for a period of time that corresponds to a plurality of cardiac cycles, (b) identify features in the power and velocity data that occur once per cardiac cycle, and (c) determine timing between the identified features.
