Abstract A technique is described for visualizing the left heart chambers with a bolus injection of radionuclide tracer using a wedged pulmonary arterial catheter. Technetium-99m as pertechnetate is injected and the heart imaged with an Anger scintillation camera interfaced to a digital computer. Time-activity curves are extracted from areas of interest coincident with the cardiac chambers and corrected for background. These curves are analyzed in two ways: high-frequency data (beat by beat ejection fraction) and low frequency data (exponential fitting to the chamber washout curve). Left ventricular ejection fraction and end-diastolic volume determined by this technique correlated with these measurements obtained from left cineventriculography. Correlation was good between the two methods of data analysis, ejection fraction and exponential curve fitting. This technique is an accurate method for measuring left heart function without performing left heart catheterization.