Many people get bad news from their own hearts in the form of a chest pains when actually getting a heart attack. But not all of these people can be treated, there are cases where angioplasty of a bypass cannot be performed. Such patients have a bad prognosis, they have a very high probability of suffering another heart attack in the near future. Dr. Esselstyn has been experimenting with a very strict plant based, fat free diet on such hopeless patients, like this one with what he claims are good results.
Now, the patients here did get medical treatment in the form of medicines, so anticoagulants, blood pressure medication, nitrates, statins etc. would all be administered where appropriate. Nevertheless, without the lifestyle changes imposed by sticking to Esselstyn's diet, most of his patients would have lived for no more than a few years, dying directly from another heart attack or from heart failure caused by subsequent heart attacks.
Now, this does not mean that we should all stick to Esselstyn's diet. More rigorous tests are needed to verify his claimed results. Also, even if verified, an intervention that can prevent a death from some cause with a period of a few years may not be good for a young person who is not facing that risk at all. Also, the short of diet Esselstyn is arguing for may lead to deficiencies on the long term if you're not very careful about your nutrient intake.
Compare this to taking aspirin. If you somehow know that you're going to have a heart attack in the near future, you'll be able to reduce the probability of getting that heart attack simply by taking an aspirin. But if you don't have that information, then taking an aspirin just in case will not help you to increase your life expectancy, because it increases the probability of a fatal intestinal bleeding, while the reduction of the probability of having a heart attack is going to have a lesser effect in this case.