A neutered, seven-year-old, female Labrador retriever was presented with complaints of tachypnea,gagging and abdominal distension. A left apical systolic murmur with an intensity of 3/6, tachycardia,weak femoral pulses and positive undulation were observed on physical examination. After echocardiographicand electrocardiographic examination, dilated cardiomyopathy (primary or secundary) andsupraventricular tachycardia were diagnosed. At a later control visit, after initiation of treatment withdigoxin, electrocardiography revealed isorhythmic atrioventricular dissociation (IAVD) and poor controlof the SVT. After transition to diltiazem, the tachycardia was well-controlled. A full recovery ofthe heart was observed on echocardiographic examination. Twenty-four months later, the dog showedno more cardiac signs. In this case report, a rare arrhythmia, i.e. IAVD in combination with SVT isdescribed. It shows the importance of SVT as a reversible cause of a DCM-like phenotype on echocardiography.