The newborn pig is currently the most used species in animal neonatal research. Valid non-invasive monitoring is important in particular for long-term survival of unsedated animals. In the unsedated newborn pig (n = 35, median age 24 h, range 7-48 h) we standardized two-dimensional Doppler echocardiography and determined the normal ranges for cardiac function. Probe positioning had to be adjusted to the V-shaped thorax and the mid-line position of the heart. Six out of the sixteen animals < 20 h had a patent ductus arteriosus compared with one of the twenty animals > 20 h old. One atrial septal defect (5 mm) and one small ventricular septal defect were diagnosed. The average heart size was 0Σ7-0Σ9 % of body weight which is similar to human infants of the same size. The mean aortic diameter was 6Σ0 ± 0Σ5 mm (mean ± S.D.) and cardiac output was 0Σ38 ± 0Σ08 l min-1; both correlate with body weight (r = 0Σ80 and 0Σ73, respectively). Tricuspid regurgitation velocity was 3Σ0 ± 0Σ4 m s-1 (mean ± S.D.), giving an estimated pressure gradient across the tricuspid valve of 37 ± 9Σ7 mmHg. The aortic diameter and the heart weight per kg body weight are comparable to those reported for preterm neonates. The cardiac output and velocities across the four valves are more comparable with term neonates.