Objective: To explore the characteristics of intra-cardiac blood cysts to provide a reference for accurate diagnosis and prognosis. Methods: In this study, 8 cases of cardiac blood cysts were analyzed retrospectively from January 2006 to March 2020, and the clinical symptoms, echocardiography, operation and prognosis were analyzed. Results: All clinical symptoms were not typical and cysts were isolated. The cysts were attached to the anterior leaflet of the mitral valve (n=4), posterior papillary muscle and chordae of mitral valve (n=1), septal leaflet of the tricuspid valve (n=2), or the tricuspid valve orifice and tricuspid anterior annulus (n=1). Echocardiography revealed the cysts were small and balloon‑like. They had high tension wall, the wall was thin and smooth. Calcification could be seen on the cyst wall. The inside was none echogenicity area and the cyst moved and swung with the valve or chordae. Of the 8 patients, 1 had no hemodynamic effects and did not need surgery. The other 7 cases were confirmed by surgery and pathology for the cardiac blood cysts. 3 subjects underwent simple cystectomy alone. 1 with infectious endocarditis and mitral valve vegetation, and the other one caused the left ventricular outflow tract obstruction. 2 subjects had a history of mitral valve abnormality with mechanical mitral valve replacement. Conclusions: Cardiac blood cysts are rare and benign heart condition in adults. They can be diagnosed by echocardiography to guide intervention.