Abstract: An apparatus for determining the magnitude of heart muscle contractions has two ultrasonic transceivers, both of which are disposed in sonic alignment on selected points of the heart. A digital counter electrically interconnects the transceivers with a digital microprocessor. The counter determines a pulse transit time which corresponds to the difference in time between the transmission of a sonic pulse from the transmitter and the reception of the sonic pulse by the receiver. Immediately after determining each pulse transit time, the counter sends the transit time signal to the microprocessor, which first filters the signals to reject any signal which indicates a heart size that is unreasonably large or small. After filtering, the transit times are averaged in groups of a predetermined number and then converted to corresponding heart size measurements for storage and display.