Kourtney Kardashian wears sexy lace-up swimsuit and Daisy Dukes for boat trip with Penelope and Mason (photos)

 Kourtney Kardashian showed off the results of her intense fitness regime in a sexy swimsuit on Sunday.

The reality star wore a plunging one-piece bathing suit as she went for a boat ride with daughter Penelope,3, and son Mason, 6, while spending the Fourth of July weekend in Miami, Florida.

The 37-year old wore a beige swimsuit with a lace-up front as she and her children were joined by sister Kim Kardashian's BFF Jonathan Cheban for a day on the water. See more pics below. ..