Echinococcosis in humans is a zoonotic infection caused by larval stages of cestode species of the Echinococcus genus. In cystic echinococcosis (CE), caused by Echinococcus granulosus, the liver is the first and the more frequent involved organ, followed by the lung. Heart, spleen, kidney and brain are usually less involved. The finding of a cyst in course of echinococcosis is usually fortuitous, during ultrasound examination, X-ray or CT. The Authors report 4 cases of human CE admitted to the Department of Infectious Diseases University of Naples "Federico II". Each case is peculiar both for the organ involved by the cysts and for the symptomatolgy. The abdominal pain, in case 1 caused by gallstones, allowed, by the ultrasound examination, to find several hydatid cysts in the liver, never symptomatic until then. The woman, in case 2, was operated for cysts in the lung, without receiving pharmacological prophylaxis. The same occurred in case 4, in which the lack of prophylaxis caused very serious relapses. In case 3, the young woman underwent an ultrasound examination because of an abdominal pain. A unique large cyst extended only in the spleen. The specific serology for immunoglobulin anti-E. granulosus resulted positive 1:61 (n.v. < 50). The Albendazole therapy caused the disappareance of pain, quickly. Later, the patient was splenectomized. It's not clear why only the spleen was involved and why the anti-E. granulosus serum levels of were increased only a little. The man, in case 4, was admitted with chest pain and electrocardiographic findings of myocardial anterior ischemia. He underwent surgical treatment of three hepatic cysts by E. granulosus, during the previous year. Two-dimensional echocardiography, transesophageal echocardiography, and cardiac magnetic resonance revealed a round cystic mass, 6 x 6 mm, located in the middle interventricular septum. The cardiac isoenzymes were in the normal ranges, but the anti-E. granulosus immunoglobulins were positive 1:5120 (n.v. < 64). The patient was treated with Albendazole. This caused the almost simultaneous disappearance of the circular cystic and clinical and electrocardiographic findings of myocardial ischemia. A cardiac hydatid cyst is an uncommon lesion, occurring in about 0.4-2% of patients with echinococcosis. In conclusion, Cystic echinococcosis is a problem in Mediterranean regions because of the high population of stray dogs, favourable conditions created by man and, above all, the illegal slaughtering.