Elvis Presley made 31 films during his career—almost all of which were wildly profitable and, creatively, mostly the same: simple romantic plots, campy humor, lots and lots of music. Released in 1964, Viva Las Vegas was built to follow the same formula for success. Yet the results were iconically different: It not only became the highest grossing film to feature Elvis, it propelled the career of costar Ann-Margret and widened the appeal of Sin City itself. What made Viva Las Vegas special? It had chemistry. It had heat. It showed larger-than-life superstars—at the peak of their powers—flirting and frolicking their way through life. Almost a decade before Elvis and Vegas became inseparable, this movie established why it was a match made in musical heaven. And the on-screen chemistry he shared with Ann-Margret wasn’t great acting—it was a real-life seduction caught on camera.