Purpose: The purpose of this study was to examine the concurrent validity of a fixated hand-held dynamometer (HHD) in comparison to a load cell in measurement of maximal isometric knee extension force in adults with congenital heart disease (CHD) and healthy adults. Methods: Fourteen adults with CHD and fourteen healthy adults were included. Each participant was tested three times with each method and the mean of the top two results for each participant and method was used in analysis. Results: The agreement between the two methods was excellent in both groups (intraclass correlation coefficient [ICC], 95% confidence interval [CI]) 0.98 (0.92-1.00) in the CHD group and ICC 0.99 (0.96-1.00) in the healthy group). There was a small difference of 19.5 Newton or 4.8% (p<.05) between the two methods in the CHD group. No significant difference was seen between the two methods in the healthy group (p>.05). Conclusions:The fixated HHD demonstrated excellent concurrent validity when compared to a load cell among adults with CHD as well as in healthy adults. Thus, in a healthy population the methods can be used interchangeably, however, a small difference between the methods is seen in the CHD group.