In this review the evidence for structural adaptations of the coronary circulation in the healthy adult heart in response to exercise and training is examined. Previously, it was thought that expansion of the coronary arteries and resistance vasculature occurred without angiogenesis. Detailed studies of the time course of coronary vascular remodelling now reveal that capillary proliferation is an integral response to exercise training, but is disguised by concurrent transformation of capillaries into arterioles by 'arteriolarization'. Increases in numbers of small arterioles <30 mum in diameter are accompanied by expansion in calibre of resistance and large coronary arteries. Stimuli related to increases in blood flow - shear stress and wall tension - and to mechanical deformation of the myocardium - stretch and compression - provide the main impetus for coronary vascular remodelling. Despite the technical difficulties of measuring such parameters in the heart in vivo, intervention studies using specific exercise components such as vasodilator, inotropic and chronotropic manipulations have allowed some insight into the differential regional effects of haemodynamic factors throughout the vascular tree. It remains to establish more clearly the involvement of mediators such as nitric oxide and growth factors in the temporal relationship to endothelial and smooth muscle growth and proliferation so that the endogenous attributes of exercise can be exploited for therapeutic purposes.