Left ventricular function before and after anatomical correction of transposition of the great arteries was assessed by computer assisted analysis of 78 echocardiographs from 27 patients obtained one year before to five years after operation. Sixteen patients had simple transposition, and 11 had complex transposition with additional large ventricular septal defect. Immediately after correction mean shortening fraction fell from 46(9)% to 33(8)%. There was a corresponding drop in normalised peak shortening rate from 5.4(3.7) to 3.3(1.1) s-1 and normal septal motion was usually absent. Systolic shortening fraction increased with time after correction and left ventricular end diastolic diameter increased appropriately for age. The preoperative rate of free wall thickening was significantly higher in simple (5.6(2.8) s-1) and complex transposition (4.5(1.8) s-1) than in controls (2.9(0.8) s-1). After operation these values remained high in both the short and long term. Thus, computer assisted analysis of left ventricular dimensions and their rates of change before and after anatomical correction showed only slight postoperative changes which tended to become normal with time. Septal motion was commonly absent after operation. This was associated with an increase in the rate of posterior wall thickening that suggested normal ventricular function associated with an altered contraction pattern. Computer assisted echocardiographic analysis may be helpful in the long term assessment of ventricular function after operation for various heart abnormalities.