Experimental studies from our laboratory demonstrated that acute cardiac rejections (AR) are associated with an increase in myocardial echo amplitudes which correlate with the histologic severity of AR. The aim of the present study was to test whether AR-induced myocardial structural changes would also alter the spatial distribution of the myocardial echo amplitudes, assessed by echocardiographic texture analysis, and whether this method would improve the sensitivity of AR diagnosis. Echocardiographic LV long axis views were daily recorded in 12 dogs after cervical heterotopic heart transplantation (mean survival time: 16.1 days; immunosuppression: cyclosporine, azathioprine and prednisolone; AR treatment: pulsed steroids) under strictly standardized conditions and digitized into a 256 x 256 x 8 pixel matrix. Texture analysis using Co-occurrence- and Run Length Matrix was performed in 45 x 12 pixel-sized regions of interest (ROI) within the septum (VS) and posterior wall (PW) in end-diastole. Results obtained without AR were then compared with those during biopsy-proven mild, moderate and severe AR. Severe AR are associated with a significant increase in Co-occurrence Matrix parameters within the septum and posterior wall (Contrast: VS: 3.1 +/- 0.7 vs. 3.9 +/- 1.1, p < 0.05. PW: 1.8 +/- 0.5 vs. 2.3 +/- 1.0, p < 0.05. Variance: VS: 19 +/- 15 vs. 36 +/- 18, p < 0.05. PW: 11 +/- 6 vs. 21 +/- 8, p < 0.01). During mild and moderate AR no significant changes in texture measurements were found. Testing the influence of ROI placement on myocardial echo amplitude, texture measurements showed a high variability in comparison to mean gray level (up to 30% vs. < 5%).(ABSTRACT TRUNCATED AT 250 WORDS)