A 
system for inducing cardioplegic arrest and performing an endovascular procedure within the heart or blood vessels of a patient. An endoaortic partitioning 
catheter has an 
inflatable balloon which occludes the 
ascending aorta when inflated. Cardioplegic fluid may be infused through a lumen of the endoaortic partitioning 
catheter to stop the heart while the patient's 
circulatory system is supported on 
cardiopulmonary bypass. One or more endovascular devices are introduced through an internal lumen of the endoaortic partitioning 
catheter to perform a diagnostic or therapeutic endovascular procedure within the heart or blood vessels of the patient. 
Surgical procedures such as 
coronary artery bypass surgery or 
heart valve replacement may be performed in conjunction with the endovascular procedure while the heart is stopped. Embodiments of the 
system are described for performing: fiberoptic angioscopy of structures within the heart and its blood vessels, valvuloplasty for correction of valvular 
stenosis in the aortic or 
mitral valve of the heart, 
angioplasty for therapeutic dilatation of coronary 
artery stenoses, coronary stenting for dilatation and stenting of coronary 
artery stenoses, 
atherectomy or endarterectomy for removal of atheromatous material from within coronary 
artery stenoses, intravascular 
ultrasonic imaging for observation of structures and diagnosis of 
disease conditions within the heart and its associated blood vessels, fiberoptic 
laser angioplasty for removal of atheromatous material from within coronary artery stenoses, transmyocardial 
revascularization using a side-firing fiberoptic 
laser catheter from within the chambers of the heart, and electrophysiological mapping and 
ablation for diagnosing and treating electrophysiological conditions of the heart.