Conventional single-beam pulsed Doppler echocardiography has certain limitations in quantitatively measuring the intracardiac blood flow, because the Doppler incident-angle to the flow stream is uncertain. In the present study, the absolute velocity and direction of the intracardiac blood flow, i.e., flow vector, were measured using our newly-developed dual-frequency two-beam pulsed Doppler echocardiography. This instrument has two transducers with center frequencies of 3.5 MHz (main-beam) and 2.2 MHz (sub-beam) which are linked by two arms. Three potentiometers are set up by the three joints to sense the relative angles. Two velocity components at the intersection of the main- and sub-Doppler beams were measured simultaneously with different directional approaches. The flow vector was calculated manually from the two velocity components. The study population consisted of 18 healthy subjects ranging in age from 23 to 39 years. The left ventricular (LV) inflow vector was measured at the center of the mitral annulus, and the ejection flow vector was measured at the levels of the tip (E1) and the mid-portion (E2) of the anterior mitral leaflet in the LV outflow tract. The results were as follows: 1. The LV rapid inflow (R) was directed slight posteriorly towards the cardiac apex, and its average maximal velocity was 78 +/- 15 cm/sec (mean +/- SD). The LV inflow due to the atrial contraction was directed even more posteriorly than was the R, and its average maximum velocity was 43 +/- 10 cm/sec. 2. The LV ejection flows at E1 and E2 were directed slightly posteriorly rather than parallel to the interventricular septum, and the maximum velocity at E1 and E2 was 53 +/- 20 m/sec and 85 +/- 23 cm/sec, respectively. In conclusion, the dual-frequency two-beam pulsed Doppler technique allows quantitative measurement of the intracardiac blood flow dynamics regardless of the Doppler incident-angle to the flow stream.