Joel can be seen grasping his chest and having a high heart rate repeatedly in The Last of Us episode 6, which indicates a heart issue.
However, this is actually a panic attack. These moments occur when Joel is told about potentially traumatic events.
The first panic attack ensues when he learns that anyone crossing the river usually ends up dead. In fear of the death of his brother, Joel begins to panic and clenches his chest.
The program’s audio, which plays the sound of a racing heartbeat, depicts this while the visuals portray a disorientated Joel. Both are common symptoms of panic attacks.
Fortunately for Joel, his brother is still alive, but you can find out what happens to Tommy later in the story here.

He starts to suffer another attack later in the episode when Joel and Ellie are confronted by the horseback riders.
This occurs because he worries Ellie could be found to have been bitten by an infected. Nonetheless, she escapes discovery, and Joel is relieved from his panic episode by the happy sounds of her playing with the dog.
As the season progresses, it will be interesting to see how our main male protagonist handles his anxieties if he survives his brutal attack, especially as he develops closer to his younger female traveler.
Already, we have seen him worry deeply about her with their bond a cause of one of his panic attacks.
The Last of Us episode 6 ends with Joel and Ellie being ambushed by an unidentified group. While critically hurt from the stabbing to his chest, Joel Miller may not survive this ordeal.