TMZ has the ONLY video of legendary watermelon-basher Gallagher leaving a Texas hospital today ... proving the only thing killer about his recent heart attack ... is the new material he came up with during his recovery.
As we previously reported, Gallagher suffered a mild-to-serious heart attack before a show last week -- and was put into a medically-induced coma.
Just a few hours ago, the comic was finally cleared to leave the hospital ... but not before cracking a few jokes on his way out.