Mycotic aneurysms are well-documented complications of infective endocarditis and occur frequently in the intracranial arteries. However, mycotic aneurysms of the coronary arteries are very rare, and there are few reports of the management of these lesions. The authors report the case of a 72-year-old woman with coagulase-negative staphylococcal endocarditis involving a perforated aortic valve, a perforated mitral valve aneurysm, and a large mycotic coronary artery aneurysm. After antimicrobial therapy, the patient underwent open-heart surgery with mitral and aortic valve replacement, coronary artery bypass, and resection of the mycotic coronary aneurysm. The authors present detailed serial echocardiograms of the mycotic coronary artery aneurysm, which was subsequently confirmed intraoperatively and pathologically.