The operation of a heart of a patient is monitored by transmitting ultrasound energy into the lungs of the patient, receiving ultrasound energy reflected from the lungs of the patient, detecting Doppler shifts in the received reflections, and processing the Doppler shifts into power and velocity data. Cardiac cycles are identified based on the power and velocity data and a determination when an identified cardiac cycle is abnormal is made. When an abnormal cardiac cycle is encountered, data corresponding to the abnormal cardiac cycle is stored. The data that was stored is eventually output. Optionally, abnormal cardiac cycles are identified using match filtering.
