Duke-NUS medical student Foo Chuan De (Class of 2029) and NUS Yong Loo Lin School of Medicine student Sendur Pandian Samiksha Kiran, both part of the Emergency Medicine Collaborative (EMCO), a tri-uni emergency medicine group, still remember the first time they heard Professor Marcus Ong speak about cardiac arrest survival.

He was not discussing intubation techniques or adrenaline doses. He was not even talking about what happens in the Emergency Department.

Instead, he spoke about the first ten minutes.

“The brain starts dying long before the ambulance arrives,” he said calmly.

It was such a simple statement. But it changed how the students saw emergency medicine.

For many medical students, Emergency Medicine is often imagined as controlled chaos: airway management, shock resuscitation, rapid decision-making under pressure. Listening to Professor Ong, however, they began to understand that the most important intervention often happens long before a doctor ever sees the patient. Survival is not won only in the resuscitation bay. It begins in the community, through bystander action, accessible AEDs and health systems designed to respond intelligently and quickly.

Professor Ong’s career is filled with moments like this: quiet reframings that change how one sees medicine.

Long before he helped build Singapore’s national resuscitation systems, he was simply a young doctor noticing things others accepted as routine. As a junior physician, he improvised tying strands of hair across scalp wounds to control bleeding. Years later, that improvisation became the now widely recognised Hair Apposition Technique. It was not flashy. It was practical, elegant and resourceful.

But it was out-of-hospital cardiac arrest that ultimately defined his work.

During Chuan De’s first clinician-scientist interview – a Duke-NUS exercise designed to help students understand what it means to be a ‘Clinician-Plus’ – Professor Ong left a strong impression. He was not only a clinician. He was also an innovator, a systems thinker and a realist.

When survival rates from cardiac arrest were dismal in the early years of Singapore’s emergency medicine landscape, Professor Ong did not simply accept them. Instead, he asked deeper questions. Not just why, but where the system was failing.

He realised that cardiac arrest survival was not merely a hospital problem. It was a systems problem.

Bystanders did not know CPR. AEDs were not easily accessible. Dispatchers were not coaching callers through life-saving steps. The chain of survival was fragile at multiple points. Rather than staying within the walls of the Emergency Department, Professor Ong stepped outward, into public health, technology and policy.

Telephone CPR. The DARE programme. The MyResponder app.

Each initiative strengthened a link in the chain.

Today, survival from out-of-hospital cardiac arrest in Singapore has increased dramatically. Thousands of families have someone still sitting at the dinner table because a nearby stranger was alerted through a mobile phone and stepped forward to help.

That is not just clinical excellence. That is systems leadership.

Yet what struck students most during their interactions with Professor Ong was not just what he built, but how he carries himself. Calm. Thoughtful. Systems-minded. He speaks about medicine as a collective endeavour or team sport, where doctors, dispatchers, policymakers, volunteers, and even app developers all play essential roles.

When Kiran asked him about what it is like to pursue Emergency Medicine, he described it as a “high risk, high-reward path, filled with critical decisional junctures.”

To illustrate, he offered a surprising example. Imagine an emergency team stopping briefly at a food court during a hectic shift. They have three minutes to order a meal. The exercise sounds trivial, even humorous. But the lesson was about triage, prioritisation, and making good decisions under pressure.

That is how Professor Ong teaches. Not by telling you what to think, but by showing you how to think.

Professor Marcus Ong has changed survival statistics in Singapore. But, on a more personal level, he changed how two young medical students understand the practice of medicine.

Emergency Medicine, Kiran and Chuan De realised, is not only about what happens when the doors burst open and the stretcher rushes in.

It is about designing a system—and a society—where fewer stretchers need to roll in at all.

And that is the most powerful kind of doctor.