This report describes for the first time a technique to collect right coronary venous blood samples from conscious dogs. Catheters, prepared from Micro-Renathane tubing, were surgically implanted in right ventricular superficial veins of three anesthetized dogs. Also implanted were an arterial catheter, a right coronary flow transducer, and a right coronary artery constrictor. The coronary catheter was introduced at a venous bifurcation so that its side holes were positioned above the bifurcation; both ends of the catheter were exteriorized. Heparinized saline was continuously infused through the venous catheter by a battery-powered pump. The dogs were maintained for 10-13 days after surgery, and all catheters remained patent. Multiple right coronary venous samples were collected from each dog. These samples were analyzed for venous oxygen tension (PvO2) under baseline conditions, with right coronary pressure reduced to 50 mmHg, and during the reactive hyperemia after release of the right coronary artery constriction. PvO2 was 27.7 +/- 1.0 mmHg at baseline, 23.4 +/- 1.0 mmHg during coronary artery constriction, and 34.3 +/- 1.5 mmHg during reactive hyperemia. These data and the position of the catheter at autopsy demonstrated that coronary venous blood had been sampled.