Robin Williams -- Pre-Op Beach Bum

3/9/2009 1:30 PM PDT BY TMZ STAFF
While he waits to undergo surgery to replace his aortic valve, Robin Williams enjoyed a peaceful walk along Miami Beach with a female friend this weekend.

The rehabbed 57-year-old was forced to suspend his one-man show tour after suffering shortness of breath last week.

No word when the heart surgery will take place.