Evidence that combined thromboxane A2 and serotonin blockade may prevent coronary artery thrombosis and the conversion from chronic to acute coronary heart disease syndromes is considered. Available data from clinical and experimental animal studies are consistent with the hypothesis that interference with thromboxane and serotonin's contributions to platelet aggregation and dynamic coronary artery constriction might prevent the conversion from chronic to acute disorders, including the development of unstable angina and myocardial infarction in some patients at risk. Substantial protection preventing the conversion from stable to unstable angina and myocardial infarction may very well require both thromboxane and serotonin receptor antagonists or the combination of a thromboxane synthesis inhibitor and receptor antagonist with a serotonin receptor antagonist. Future clinical studies should test this hypothesis directly.