Background: Primary cardiac tumours are rare, and diagnosis may be difficult, as symptoms and cardiac imaging may mimic other cardiac diseases. The intimal sarcoma is the least commonly reported cardiac tumour with only few cases reported worldwide. In this case report, we present a case of an intimal sarcoma with a highly aggressive disease course. Case summary: A 60-year-old male with a history of prior aortoplasty due to congenital aortic stenosis, mechanical aortic valve replacement, and aortic stenting due to aortic dilatation presented with night sweats, malaise, and dyspnoea. Initial imaging (including transthoracic and transoesophageal echocardiography and emergency computed tomography) revealed masses suspected to be thrombi in the left atrium and ventricle. However, a positron emission tomography/computed tomography scan revealed that the masses were suspicious for malignancy. The patient underwent non-radical tumour resection and insertion of biological valve prostheses. Subsequent tissue analysis and pathology assessment revealed an intimal sarcoma. There were no curative treatment options, and the patient succumbed to his illness <3 months after surgery. Discussion: This case report presents a case of a highly aggressive intimal sarcoma. As complete tumour resection is of great importance when it comes to life expectancy in cardiac sarcomas, early diagnosis using non-invasive and invasive imaging modalities is essential to start early treatment and to improve outcomes in this patient group.