The Leboyer birth method requires that the newborn infant is placed on the mothers abdomen and the cord is clamped when it stops pulsating. Since late cord-clamping may result in marked hypervolemia and polycythemia of the neonate, we studied right and left ventricular systolic time intervals by means of pulsed-Doppler echocardiography. Left and right ventricular preejection periods (LPEP, RPEP), right time peak velocity (RTPV), left and right ventricular ejection times (LVET, RVET), and ratio of RTPV/RVET(c) corrected for heart rate were studied in 15 fullterm neonates with early (< 10s) cord clamping and in 15 fullterm neonates delivered according to Leboyer (cord clamping after 3 min) on day 1 (2-4 h after birth) and day 5. After Leboyer birth hematocrit was significantly increased on day 1 (0.61 +/- 0.06 vs. 0.53 +/- 0.07) and on day 5 (0.57 +/- 0.02 vs. 0.50 +/- 0.07). Blood pressure was similar in both groups and increased by about 10% from day 1 to day 5. LVET and RVET were not affected by the mode of placental transfusion, thereby suggesting normal left and right ventricular function after Leboyer birth. The LPEP/LVET (0.36 +/- 0.09 vs. 0.30 +/- 0.08) and RPEP/RVET ratio (0.41 +/- 0.11 vs. 0.33 +/- 0.08) were significantly higher in the Leboyer group (p < 0.05) compared to the early cord clamped group suggesting higher systemic and pulmonary resistance. RPEP decreased significantly by 17% in the control group from day 1 to day 5 (p < 0.05), but did not change in the Leboyer group. In the Leboyer group RPEP/RVET ratio decreased significantly from day 1 to day 5, whereas the control values did not change during the first five days. RTPV:RVET(c) is inversely related to pulmonary artery pressure. A normal ratio is > 0.35, or greater. Mean ratio of RTPV : RVET(c) was significantly lower in the Leboyer group (0.31 +/- 0.08) on day 1 compared to the control group (0.41 +/- 0.09; p < 0.05), but did not differ on day 5. The results suggest that Leboyer delivery was associated with transiently increased pulmonary and systemic resistance, whereas right and left ventricular functions were not affected. This may be explained by increased blood viscosity due to increased hematocrit.