I know in pre Vatican II, when we said “I confess” we struck our breast three times as you are seeing. If you read the gospel account of the Pharisee and the Publican that Christ told, the Pharisee stood in the temple and extolled his righteousness, whereas the publican (the sinful common man) stood in the rear of the temple and did not even raise his eyes to God and admitted his sin and asked for forgiveness from God. There were some translations that had him striking his breast three times as an expression of sorrow/penance/ mortification. In the old missals that were used in the Latin Mass I remember that printed at the point when the words “through my fault, through my fault, through my most grievous fault” we were to strike our breast three times. That custom has remained but it is an act of devotion and while encouraged, it is not mandatory.
If you do not strike your breast/heart like others, there is no sin and no fault. Be at peace with that. It is a devotion, not a dogma or doctrine of the church.