Sixteen patients surviving orthotopic cardiac transplantation were studied by M-Mode and two dimensional echocardiography (ECHO) on the same day of cardiac biopsy during (n = 138) a mean follow-up of 6.2 +/- 4 months (range 1-4 months). The following parameters were measured: right ventricular end diastolic internal diameter (RVdD) left ventricular end diastolic internal diameter (LVdD), interventricular septum (IVS) and posterior wall (PW) diastolic thickness, myocardial mass (MM); LV cross sectional area (CSA) and ejection fraction (EF). LV and RV wall motion, pericardial effusion and myocardial echogenicity (brightness) were evaluated by inspection. Every ECHO was compared with the previous one for qualitative and quantitative changes. In the absence of rejection, analysis of the data during the first postoperative week showed the following results: mean EF = 51 +/- 6.8%, dilated overloaded RV (30.4 +/- 4.8 mm), various amount of pericardial effusion; FE increased significantly (55.3 +/- 4%; p less than 0.001) and RVdD decreased (26.6 +/- 5mm; p less than 0.001) after the 2nd week and remained stable thereafter, while pericardial effusion decreased or disappeared. The mean values of the remaining ECHO parameters did not very significantly during the follow-up.(ABSTRACT TRUNCATED AT 250 WORDS)