Objective: To compare measurements of regional myocardial blood flow volume between microsphere measurement of regional flow (0.5- to 2-g tissue sampling) and a potential alternative measure, local flow (1 mm(3)) in the microcirculation measured by laser-Doppler perfusion monitor. Design: Prospective, randomized, controlled. Setting: University research laboratory. Participants: Pigs. Interventions: After anesthetization, in 5 pigs (25 to 30 kg), the left anterior descending coronary artery was isolated and its resting Row measured by a perivascular-Doppler flowmeter. Left ventricular pressure and first time derivative of left ventricular pressure were measured. The laser-Doppler probe needle (type N) (Model ALF-21, Transonic Systems, Inc, Ithaca, NY) was inserted 2 to 3 mm into the wall of the left ventricle, parallel to the coronary artery. All 5 pigs were subjected to 0 (control), 50%, 75%, and 100% constriction of the left anterior coronary artery. Measurements and Main Results: Measurements by radioactive microspheres correlated poorly with those by laser-Doppler and extremely poorly with those by perivascular Doppler flowmeter. For percent change from baseline in the constricted arterial zone, radioactive measurements correlated well with those by laser-Doppler but not those by Doppler flowmeter. Also, radioactive measurements of percent change in flow in the circumflex (nonconstricted) zone and laser-Doppler measurements in the constricted arterial zone did not correlate well. Conclusions: Laser Doppler can be recommended for experimental research to monitor local few. These measurement may relate to change in regional flow during normal perfusion and hypoperfusion. Before the laser Doppler perfusion monitor can be used clinically, tissue trauma from the 0.55-mm needle needs to be evaluated. Copyright (C) 1996 by W.B. Saunders Company. [References: 32].