In this paper, the microstructure and ultrastructure of zebrafish heart were observed by light microscopy and transmission electron microscopy. The results showed that the heart of zebrafish was composed of four parts:ventricle, atrium, bulbous arterious and venous sinus. The ventricle is brown-red and the stratification was obvious, it was divided into a compact layer of the epicardial region and a sponge layer of the endocardial region. The atrium is bright red and consists only of a loose sponge layer. An arterial trunk (abdominal aorta) was issued in front of the ventricle and the starting part of the arterial trunk expands into ellipsoidal shape, called the bulbous arterious. The bulbous arterious was pear-shaped, which can be divided into three layers from the inside to the outside, and they were the inner layer, the middle layer and the outer layer respectively. The venous sinus was difficult to isolate separately, therefore, the sinus was not isolated and observed separately. In this paper, the presence of telocyte interstitial cells was observed in the ventricles, atrium and arterial spheres. Their morphology was slender and long and could be divided into podomeres and podoms. The presence of multivesicular bodies was observed in the cardiomyocytes of the ventricles, which were often distributed on the outer edge of the cardiomyocytes, close to the sarcolemma or adjacent to the mitochondria of the outer edge of the cardiomyocytes.