Objective This study aims to research the effect of the increased interstitial fluid accumulation in patients with congestive heart failure on the diffusion capacity of the alveolar-capillary membrane. Methods This prospective study is conducted on 77 in-patients diagnosed with pulmonary edema and decompansated heart failure. The B-line counts of the patients are calculated through echocardiography and thoracic ultrasonography within the first 24 hours of their admission and the patients are categorized into two groups based on their B-line counts being higher or lower than 15. After sufficient diuretic treatment, the patients are subjected to respiratory function test, diffusion test(DLCO) and 6 minute walk test. Results The following results in study have been found in the echocardiography of the patients in the higher-than-15 B-line group: lower RVEF (p=0,003), lower RVSm (p=0,014), higher SPAP (p<0,0001), higher TRV (p=0,001), more dilated VCI radius (p<0,0001), higher LA volume(p=0,007), higher E/e’>15 (p<0,0001), higher pleural effusıon (p=0,014). The following results have been found in the respiratory function test, DLCO and 6 minute walk test of the patients in the higher-than-15 B-line group: lower FVC (p <0,0001),lower FEV1 (p=0,002), lower corrected DLCO (p<0,0001), lower 6 minute walk test (p<0,0001).16 of the 77 patients have undergone right heart catheterization during their stay in the hospital and higher PVR (p=0,039) has been found in the higher-than-15 B-line group. Conclusion B-line counts of higher than 15 may be predictor of decrease in diffusion capacity, restrictive patern in respiratory function, decrease in right ventricular function and increase in pulmonary vascular resistance.