Background: Acute myocardial infarction (AMI) is a social burden.However, being able to predict AMI could lead to prevention.It is difficult to predict AMI in coronary angiography.A previous study showed only the relation between the lunar phase and the occurrence of AMI, but the period it takes for the moon to orbit around the earth and the period of the lunar phase differ.This study investigated the effect of the gravitation of the moon on AMI.Methods: Data was comprised of 1369 consecutive patients with first AMI at 5 hospitals from October, 1984 to December, 1997.The universal gravitation of the moon was calculated and compared to the earth onset time of AMI.Universal gravitation of the moon was derived by G x m/d2 (G: universal gravitation constant, m: the mass of the moond: the distance between the center of the moon and the center of the earth).Results: The relationship between m/d2 and the cases of AMI was determined.There was an increase in cases, when there is a distance of more than 399864 km from the center of the earth to the center of the moon.The gravitation of more than 399864 km was determined to be weaker gravitation.It is confirmed that the number of AMI patients significantly increases at weaker gravitation periods in this multicenter trial.Conclusions: In conclusion, these results suggest that the gravitation of the moon may have an influence on the occurrence of AMI.