The scientists looked for coronary artery calcium or "CAC" - which is a sign of clogged up blood vessels and risk of a heart attack.
The scientists scanned 705 people's hearts in a CT scanner after teaming up with a research group scanning mummified bodies.
At the age of 45, almost no Tsimane had CAC in their arteries while 25% of Americans do.
By the time they reach age 75, two-thirds of Tsimane are CAC-free compared with the overwhelming majority of Americans (80%) having signs of CAC.
The researchers have been studying this group for a long time so it is not simply a case of the unhealthy Tsimane dying young.
Michael Gurven, a professor of anthropology at University of California, Santa Barbara, told the BBC: "It is much lower than in every other population where data exists.
"The closest were Japanese women, but it's still a different ballpark altogether."