Drug and device therapy for heart failure is increasingly determined based on left ventricular ejection fraction. Significant disparity frequently exists between echocardiographic and nuclear scintigraphic techniques, even when testing is performed nearly simultaneously in clinically stable patients. In 119 patients with left ventricular dysfunction who underwent both echocardiography and stress testing with nuclear imaging within seven days (but with significant disparity in reported left ventricular ejection fraction), we identified four clinical variables which were associated with left ventricular ejection fraction difference. These clinical variables included atrial fibrillation, left ventricular hypertrophy, severe mitral regurgitation and paced rhythm.