Atrial fibrillation is the most common pathologic supraventricular tachycardia. It has many causes, is an expensive disease, impairs quality of life and leads to an increased risk of death. Atrial dissociation is characterised by the presence of two independent sets of P-waves. This peculiar abnormality may give rise to the scenario where one atrium is in atrial fibrillation while the other is in sinus rhythm. This is the first published case of atrial dissociation where the phenomenon is demonstrated by transmitral and transtricuspid pulsed wave Doppler.