The atrial myocardial cell in three teleostean speciesGadiculus thoriJ. Smith,Melanogrammus aeglefinus(L.) andOnos cimbriusL. is described. The contractile material is located in the periphery of the cell, whereas the nucleus and mitochondria occupy the central part. The tubules of the sarcoplasmic reticulum are of larger diameter at the Z‐band levels than elsewhere in the sarcomere. The transverse part of the intercalated disc is composed of alternating desmosomes and intermediate junctions. In the longitudinal part of the disc desmosomes occur, situated in close proximity to Z‐bands. Short nexuses were found in the longitudinal part of the disc, usually near the transverse part. InG. thorinumerous atrial specific granules were seen. A high number of mitochondrial granules and glycogen granules seems to occur inO. cimbrius.In the atrial myocardial cell of two or six day‐old larvae ofM. aeglefinus.the contractile material is organized into thin myofibrils, and numerous ribosomes are located in the sarcoplasm.The results of the present work are compared to those previously described in the teleostean atrium and ventricle. The differences in the heart structure within the gadoid family are discussed from a functional and an evolutionary point of