Most of clinical morbidity in cardiology are associated with abnormalities of the left ventricle. Several methods have been developed to measure the left ventricular function, including cardiac catheterization with cineangiography, echocardiography, and systolic time interval. But these methods have many limitations. ECG gated cardiac blood pool scan provides a safe, noninvasive, repeatable method for determining the left ventricular function. Utilizing the cardiac blood pool scan, we measured the left ventricular function in 165 cardiac patients, and in 26 normal subject. 1. Left ventricular ejection fractions were measured by cardiac blood pool scan, and compared in 20 patients with that measured by x-ray cineangiography. Correlation coefficient was 0.885. 2. Ejection fractions were classified by funtional class made in New York Heart Association. Ejection fractions well represented the functional status. 3. Ejection fractions decreased in cardiomyopathy ($20.1{pm}4.8%$) and ischemic heart disease ($34.4{pm}16.7%$). Impaired ejection fractions in myocardial infarction were associated with the extent of infarction. 4. Regional left ventricular wall motion was evaluated from the end-diastolic and end-systolic images. In cardiomyopathy diffuse hypokinesia was noted and in myocardial infarction akinesia was noted on the infarcted areas.