Primary cardiac angiosarcoma is a very rare and fast-growing tumour, where the coincidence of pregnancy and primary cardiac angiosarcoma is extremely rare. This makes diagnosis difficult and sometimes late, resulting in a poor prognosis from the moment of detection. We present the case of a 38-year-old pregnant woman in the 16th week of gestation diagnosed with obstetric antiphospholipid syndrome who came to the emergency department with asthenia, dyspnea, tachycardia and hypotension. A transthoracic ultrasound was performed with a diagnosis of pericardial tamponade. She was admitted to the intensive care unit for extrinsic cardiogenic shock. Transesophageal echography was performed, showing a large variegated mass in the right atrium, raising the differential diagnosis between atrial thrombus and myocardial tumour. Elective cesarean section was performed at 22 weeks of gestation. Months later, the patient was readmitted with a very unfavorable clinical evolution, experiencing diffuse alveolar hemorrhage/vasculitis refractory to life support measures. It was agreed to limit the therapeutic effort while awaiting the anatomopathological report of intracardiac biposia, subsequently confirming the histological nature of cardiac angiosarcoma. This case report highlights its rarity, showing a non-specific clinical presentation, which directed us towards a thrombosis in the right atrium and the fatal prognosis of angiosarcoma, mainly related to the progression of the disease due to a late diagnosis.