The South African double Olympic champion scored an easy victory in the women's 200 metres breaststroke.
Heyns clocked 2min 28sec, well short of the world record 2:23.64 she set at last month's Pan Pacific Championships in Sydney but still a Games record.
"I'm glad it's over," she said. "This was the one I was worried about because of the altitude."
The 24-year-old says she aims to go faster at next year's Sydney Olympics. Her performance spearheaded the hosts' dominance in the pool.
The bravest swimming performance so far, however, has been from Zimbabwean disabled swimmer Toddy Mudzenjerere. The 34-year-old, disabled by polio, took 4min 23.76sec to swim a one-length race in the 50-metre Ellis Park pool in one of the most emotional moments of the Games so far. "I just wanted to be part of the Games," Mudzenjerere said after his feat.
The acting African hockey president, Steve Jaspan, was robbed of his wallet and cellular phone on Sunday while on the way from his Johannesburg home to the Games. This follows Friday's carjacking of an official Games vehicle in Soweto.Reuse content