AT 1.83m and weighing 75kg, police Senior Staff Sergeant Dennis Kok Cheak Boon looked the picture of health - but the martial arts expert had three blocked arteries.

They proved fatal for the father of two when he collapsed during a taekwondo class he was taking part in with his six-year-old daughter at the void deck of Block 638, Woodlands Drive 75 on Thursday.

Senior Staff Sgt Kok, 31, who was due to take his black tip taekwondo test today, fainted after being kicked in the abdomen by his sparring partner. He was wearing a protective guard at the time.

His wife, Madam Tan, 32, was cycling towards Block 638 with her five-year-old son and a bag of freshly baked muffins for her husband and daughter when a friend called to tell her that her husband had fainted.

When Madam Tan arrived, the taekwondo coach was performing cardiopulmonary resuscitation on her husband, an 11-year veteran of the police.

'He was lying unconscious on the floor but his hands and chest were still moving when I touched him,' she said.

An only son, Senior Staff Sgt Kok died at the Tan Tock Seng Hospital. Doctors told Madam Tan the heart attack struck when her husband's blocked arteries burst.

Madam Tan said her husband had never complained of chest pains or that he was feeling unwell. But she told The Sunday Times that both his parents had similar sudden deaths: his father of a heart attack when Senior Staff Sgt Kok was only a year old and his mother from high blood pressure.

Knowing his family history, Madam Tan constantly reminded her husband to be vigilant with his health.

Senior Staff Sgt Kok assured her that he went for the regular checks required by the police and that he also jogged and did other exercise regularly.

'The reports always came back normal, but now this,' said Madam Tan.

Senior Staff Sgt Kok's colleagues at the Queenstown Neighbourhood Police Centre described him as a 'loving family man who never lost his temper'.

Mrs Tan Cai Yong, his mother-in-law, said: 'He left so suddenly, now we're all heartbroken.'