Normally he pulls tired nippers out of the water in training, but the real thing was quite shocking for him, he said.
"It really took me by surprise how quick everything like that happens."
Van Den Heuvel said with "sky high" adrenaline his instincts just kicked in when he jumped off the front of the boat, but he was a bit worried about ending up in trouble himself.
"Afterwards, for the next few hours I was shaking like couldn't stop shaking because of the adrenaline."
He said the IRBs (inflatable rescue boats) are crucial for surf clubs, and without one on Sunday, it would have been a very different result.
Lifeguards are expecting one of New Zealand's biggest summers with everyone travelling in their own backyards.
Titahi Bay's lifesaving co-ordinator Georgia McLaren said the girls were extremely fortunate, because if it wasn't for the refresher course there wouldn't have been anyone there to help, with patrols not starting until December.
She said if Van Den Heuvel hadn't made the split-second decision to dive into the water, the third girl would have drowned.
"She'd given up, no energy left and was under the water.
"Mac was quite scared really but acted in that adrenaline and just thought 'I have to go do this' and saw she was in serious trouble."
McLaren said this could have been a tragedy which serves as a reminder about beach safety.
"When you've got kids with you, keep an eye on them, keep them in arm's reach and don't overestimate your ability in the water to be able to cope in the conditions.
"In this case they didn't know their limits ... but the key message in it, is that they also didn't know how to recognise the rip, and that was the reason they got swept out."
Remember these beach basics
• Choose a beach with a lifeguard and swim between the red and yellow flags • If caught in a rip, remember the 3Rs rip survival plan: relax and float to conserve energy; raise your hand to signal for help; and ride the rip until it stops and you can swim back to shore or help arrives • Look for, read and understand the safety signs - ask a surf lifeguard for advice as beach conditions change • Always keep a very close eye on young children in or near the water. Keep children within arm's reach at all times • Know your limits. Don't overestimate your ability in the water or your children's ability to cope in the conditions • Never swim, fish or surf alone • If in doubt, stay out of the water • When fishing from rocks, always wear a lifejacket and shoes with grip and don't turn your back to the sea • If you see someone in trouble, call 111 and ask for the police as they have a direct line to surf lifesavers
- Information courtesy of the Surf Lifesaving Association