SUMMARY Several methods have been used to measure left ventricular regional blood flow in humans. However, limitations and lack of validation in patients are major problems. A continuous thermodilution technique to measure regional left ventricular blood flow in patients with coronary disease was validated in vivo. This technique permits simultaneous assessment of venous blood flow draining predominantly from the anterior wall and of the total left ventricular effluent. Thermodilution measurements with simultaneous electromagnetic flowmeter recordings from anterior descending vein grafts were compared in patients with occluded or subtotally occluded anterior descending coronary arteries. The thermodilution method yielded values for both absolute anterior regional blood flow and changes in anterior regional flow that compared closely to anterior descending bypass graft flow measured independently. The multithermistor technique may be useful in monitoring flow effects of regional coronary disease over time, as well as in studies of agents purported to alter regional blood flow.