They also knew that coronary artery surgery, in which unobstructed blood vessels from elsewhere in the body were used to bypass the affected areas, relieved the angina. So did angioplasty, introduced in the late 1970’s, in which doctors used balloons and stents to clean out and keep open clogged arteries.

So it made sense to conclude that bypassing or opening diseased blood vessels would also prevent heart attacks (during which there is complete occlusion of a particular vessel and resultant death of heart tissue). Once vessels became about 95 percent occluded, doctors believed, a tiny blood clot could obstruct them entirely. Alleviating obstructions became the gospel for prevention.

As early as the 1930’s, however, there were naysayers. Some physicians believed heart attacks resulted from some type of rupture within the vessel; how much occlusion was present did not matter. Over the succeeding decades, researchers confirmed that this theory was indeed true. The rupture of plaques containing fat, cholesterol, calcium, and other substances caused heart attacks. Drugs such as statins that lowered cholesterol levels and stabilized these plaques, thus prevented heart attacks.

Yet, as Jones describes, cardiologists have been remarkably slow to abandon the old hypothesis, continuing to perform hundreds of thousands of bypass operations and angioplasties annually not only in the setting of heart attacks (when they are appropriate) but also to try to prevent them. In his book, Jones points out that a 2011 study found that as many as 85 percent of angioplasties were elective and non-emergent.

Jones readily admits there are financial reasons for the continued use of these procedures. Bypass and angioplasty make money for physicians and hospitals. But other explanations—what he terms “emotional and psychological”—are more interesting and especially relevant to current debates about treating high cholesterol and hypertension.

In the case of cholesterol, the new guidelines, promulgated by a joint American College of Cardiology-American Heart Association task force, discourage the standard practice of checking patients’ cholesterol counts and choosing among a series of medications to lower them to specific levels. Instead, the group recommends treating all patients who fall into specific risk groups with a particular agent—the statins—and not following their levels.

In the case of hypertension, a committee convened by the Joint National Commission raised the acceptable levels of blood pressure. For example, a blood pressure of 150/90, formerly thought to be too high, is now considered adequate for patients 60 and older. For patients with diabetes and kidney disease, doctors need no longer shoot for a blood pressure of 130/80. Rather, 140/90 is acceptable. For both high cholesterol and hypertension, the new recommendations reflect the best available data from randomized controlled trials.