You should get a follow-up exam. Sometimes, the sternum (center bone that connects the rib cage) healing process is compromised and infection can set in, etc. It can be serious as there can be lost bone and structual damage.
For some statistics, infection resulting from wound complications has been sited as a small issue with the median sternotomy procedure. Among a consecutive series of 9,279 sternotomies performed during a period of 2½ years, 61 (0.66%) patients developed significant wound complications. Of these, 58 (95.1%) survived. Sternal infection occurred in 36 patients (0.39%). Predisposing factors included chronic obstructive pulmonary disease, diabetes mellitus, obesity, closed chest massage, prolonged assisted ventilation, and excessive bleeding after operation.
There should be significant healing after 6 months.