Tricuspid and mitral valve regurgitation are commonly observed in patients after orthotopic cardiac transplantation (HTX). The etiology is still controversial. Aim of the present study was to assess the degree of regurgitation and its etiology. Twenty-five patients (mean age 47.9 +/- 11.8 years) undergoing HTX were studied intraoperatively by transesophageal echocardiography. The degree of tricuspid and mitral valve regurgitation was assessed by planimetry of maximum systolic area of the regurgitant jet (JA). The cross-sectional area of right and left atrium and the recipient (R) and the donor (D) cross-sectional area of the atria, and their ratio (R/D) were assessed by two-dimensional echocardiography. The following preoperative and perioperative hemodynamic parameters were measured: systemic arterial pressure, cardiac index, pulmonary artery pressure, and pulmonary vascular resistance. Tricuspid regurgitation was found in 21/25 (84%) patients, mitral regurgitation in 12/25 (48%). The degree of mitral regurgitation showed no correlation to any of the studied parameters. Tricuspid regurgitation showed no correlation to the hemodynamic parameters, but showed significant correlation to R/D ratio (JA versus R/D: r = 0.90; SEE = 0.2) and to the dimensions of the recipient atrium (JA versus R: r = 0.89; SEE = 1.9). Three patients who underwent bicaval anastomoses did not show tricuspid regurgitation. In conclusion, tricuspid regurgitation has a higher prevalence than mitral regurgitation and occurs in most patients immediately after HTX; mitral regurgitation was less frequent than tricuspid regurgitation and was not correlated to the hemodynamic parameters or to the distortion of atrial geometry; tricuspid regurgitation was significantly correlated to the ratio of recipient/donor right atrium; surgical techniques reducing the recipient atrium may decrease the occurrence and the degree of tricuspid regurgitation.