An eight-week-old female Cavalier King Charles spaniel was presented with tachypnoea, pyrexia and distended jugular veins following bite injuries to the chest and abdomen. Pericardial effusion was suspected from clinical, electrocardiographic and radiographic findings, and confirmed by echocardiography. Pericardiocentesis was carried out and the purulent fluid aspirated yielded Pasteurella multocida on culture. After drainage, broad spectrum antibiotic therapy was instituted and the puppy went on to make an excellent clinical recovery. Despite this, some hyperechoic areas of myocardium were observed on echocardiography and occasional ventricular premature complexes were seen on electrocardiography. These were probably the result of an associated myocarditis.