The Tsimane, a society of hunter-gatherers, have the lowest-ever recorded levels of clogged arteries among any population studied, new research found.
Scientists say the finding points to the importance of reducing risk factors for heart disease.
The Tsimane are physically active - exercising for about four to seven hours every day - and their diet is low in fat and sugar. They also don't smoke or drink often.
"The average middle-aged Tsimane has arteries that are about 28 years younger than those of Westerners," said Dr Randall Thompson, a cardiologist at St Luke's Health System in Kansas City, Missouri, who helped lead the research.
The study was published online on Friday in the journal Lancet and presented at a meeting of the American College of Cardiology.
Thompson and colleagues teamed up with anthropologists who have been tracking the Tsimane for years for glimpses into their health.
The Tsimane, a group of about 16,000 people who live along a tributary of the Amazon, are one of the best-studied Indigenous groups in the world.
The 705 participants in the study spent a day paddling in their canoes and then hopped a six-hour Jeep ride to the nearest city, so doctors could take computer scans of their hearts and measure their weight, heart rate, blood pressure, cholesterol and blood sugar.
The Tsimane's health results were then compared to a sample of more than 6800 Americans. Scientists concluded Americans were five times likelier to have heart disease than the Tsimane. Almost nine in 10 Tsimane had no risk of heart disease.
Lifestyle probably plays a bigger role than genetics in avoiding heart disease, Thompson said.
He noted that as the Tsimane are gradually introduced to processed foods and motorised canoes, their cholesterol levels have slowly increased.