Cardiac-type fatty acid-binding protein (cFABP) from human heart muscle of three individuals was isolated and characterized as pI 5.3-cFABP. The proteins were structurally analyzed by tryptic peptide mapping, application of plasma desorption time-of-flight mass spectrometry and amino acid sequencing. All three preparations of human heart FABP, having 132 amino acids, differed from the published sequence [Offner et al. Biochem J 251: 191-198, 1988] in position 104, where Leu is found instead of Lys, and in position 124, where Cys is found instead of Ser.