Coronary spasm was observed in two sisters. Neither of them had significant atheromatous stenosis in the coronary arteries. The 41-year-old elder sister presented with resting morning angina. The stress electrocardiogram showed marked depression of the ST-segment in precordial leads. Diffuse vasospasm in the left anterior descending artery was induced by the intracoronary administration of acetylcholine. The 38-year-old younger sister suffered from acute inferior myocardial infarction after taking methylergonovine following an abortion. Emergent coronary angiography disclosed a thrombus in the proximal right coronary artery which was dissolved with intracoronary administration of urokinase. There was no residual stenosis in the culprit vessel. Although the sisters do have risk factors for coronary spasm, an inherited factor may contribute to the mechanism of the spasm.