There are two tendons in a chicken breast, one in the small fillet and one in the main breast. Removing them is not essential, but it does make for easier slicing and eating. In step 2, the main sinew is removed prior to slicing strips for stir-frying.
Pull away the small fillet. Cut out the tendon with a chef’s knife.
Cut away the tendon from the breast, using a cleaver or chef’s knife.