Emmy-winning TV icon John Ritter, best known for his role as endearingly awkward Jack Tripper in Three's Company and more recently the star of ABC's family comedy 8 Simple Rules for Dating My Teenage Daughter, died Thursday of a heart problem. He was 54. According to reports, Ritter had an undiagnosed defect in his aorta. In a statement, ABC said it was "shocked and heartbroken at the terrible news of John's passing. Our thoughts and prayers are with his wife and children at this very difficult time." There's no word on what impact Ritter's death will have on 8 Simple Rules, which was slated to kick off its second season Sept. 23. Ritter is survived by his wife, Wings actress Amy Yasbeck, as well as children Jason, Carly, Tyler and Stella. For a tribute from TV Guide critic Matt Roush, click here.