Abstract Background Intracardiac thrombosis is a relatively common pathological condition. Often, it is diagnosed at echocardiography during the subacute or chronic phase. In the very acute phase, tissue composition can make thrombus appearance very different from that usually seen. Fresh thrombosis has been previously found also in peripartum cardiomyopathy (PPC), but with imaging features different from our case. Case summary A 27-year-old woman was referred to our hospital for PPC, with echocardiographic finding of intraventricular masses, resembling big bubbles. Cardiac magnetic resonance (CMR) allowed definitively diagnosing intracardiac ‘very acute’ thrombosis, which is rarely detected. Discussion Our case provides a practical lesson about management of an unusual presentation of a common problem. When early echocardiography does not allow making a certain diagnosis, CMR can be helpful and decisive, due to its unique ability to provide characterization of intracardiac masses.