A 41‐year‐old man presenting with unstable angina was found to have diffuse coronary ectasia with a partially occluding thrombus in the proximal left anterior descending artery. Anticoagulation with heparin followed by warfarin resulted in relief of angina and resolution of thrombosis at follow‐up angiography 3.5 months later. The patient remains well after three years. Nonatherosclerotic ectatic coronary arteries are prone to thrombosis possibly because of spasm, intimal damage, and blood current eddies. We believe that chronic warfarin therapy may be indicated in many patients with coronary ectasia.