1. The main cause of underestimation of p[O.sub.2] in Arterialised capillary blood was insufficient arterialisation leading to a venous admixture, the effect of which depends upon the arteriovenous p[O.sub.2] difference.

2. Percutaneous in situ venous arterialisation (PICVA) follows this surgical experience, using a series of unique catheter-based devices to Arterialise isolated segments of coronary vein to provide retrograde perfusion of the ischaemic myocardium.