Acute myocardial infarction (AMI) was rare a century ago and was diagnosed in few living patients prior to 1925. By 1950, it was the most common heart problem seen by clinicians. Thought at first to have been overlooked, there were many explanations offered for its neglect. Smoking, hypertension, and elevated cholesterol are associated with AMI, but of these only smoking should be considered a cause. Hypertension and hypercholesterolemia may be co-effects, perhaps of inflammation stimulated in the lung and blood vessels by smoking and air pollution, thus affecting vessels and arteries subjected to systemic blood pressure. Air pollution--the 20th century's other "big smoke"--deserves consideration as a 2nd cause. Auto exhaust blankets the world's cities. It consists of smoke and other effluents of petroleum vaporization and combustion that emanate from the crankcases and exhaust pipes of trucks and automobiles. The major living spaces (conurbations) of the world now imitate and exceed Los Angeles in their levels of air pollution. Auto exhaust gases fit the timeline, and their increasing amounts parallel the worldwide rise in coronary heart disease. Increasing doses of these chemicals imitate cigarette smoke and stimulate inflammation in the lungs. They appear to be absorbed into the blood, where they cause inflammation in blood vessels, increased blood pressure, and clogged coronary arteries. Avoidance is the obvious solution. Quit inhaling cigarette smoke and motor vehicle exhaust. The benefits have been shown and can be proved by intervention. The quest for clean air is hygienic-like avoiding water contaminated with feces was 150 yr ago. Clear air must be made a moral right. Its attainment requires a major revolution in priorities for energy use and lifestyle. Two types of smoke must be avoided. The world's most lethal disease.