Congestive heart failure denotes the disturbance of the ability of the heart to maintain an adequate blood flow to the tissues and organs. It was confirmed that the cardiac output was reduced in severe congestive heart failure but if the clinical symptoms were improved after the treatment, the cardiac output was increased. The extrarenal disturbances such as congestive heart failure probably influence the kidney by causing a reduction in renal blood flow sufficient to reduce renal function but they do not produce anatomic injury and so. Consequently the renal decompression has been termed reversible uremia or functional renal failure. A reduction in glomerular filtration rate and renal blood flow is the basis for the rise in serum creatinine in prerenal failure. I would like to publish this paper because there were a few reports about the serum urea nitrogen and creatinine in chronic congestive heart failure. Serum NPN, BUN and creatinine values in 150 patients with chronic congestive heart failure, who were admitted in Busan university Hospital between 1965 and 1975, were measured on the admission and after the treatment for the congestive heart failure. The range of the serum NPN was 15~121mg% in 119 cases with congestive heart failure and 44 of them (36.97%) had the serum NPN above 30mg%. The range of serum BUN 7.5~103mg% in 129 cases and the serum BUN was above 20mg% in 49 of them (37.98%). The range of the creatinine was 0.15~20mg% in 146 cases and the serum creatinine was above 1.25mg% in 47 of them (32.19%). After the treatment for the congestive heart failure, the serum NPN, BUN and creatinine returned to the normal value. None had the increased serum NPN, BUN and creatinine among the left heart failure, but the serum NPN, BUN and creatinine were increased only among the left and right heart failure.