The myocardial perfusion and left ventricular function were evaluated by bicycle ergometry and myocardial scintigraphy in 23 patients with primary angina taking into account the status of coronary collateral circulation in response to stenotic and occlusive atherosclerosis. In addition to severe occlusive disease of the coronary bed, most patients had significant disturbances of myocardial perfusion and left ventricular function, which were detected during exercise tests. In patients with compensatory collateral circulation in the coronary bed, such disturbances were less marked than in those without anastomoses. However collateral coronary circulation cannot be regarded to be of real value as it compensates impaired perfusion incompletely, but in some cases it can result in impaired myocardial vascularization apparently due to the steal syndrome.