Heart disease in the Boxer was initially documented in the 1980s and referred to as a Boxer cardiomyopathy. More recent studies have confirmed that this disease is inherited and is primarily characterized by disturbances in the cardiac electrical system, fainting episodes and sudden death. The inherited nature of the disease has led to increased interest in the screening of dogs for the disease by electrocardiogram, ultrasound and Holter monitoring prior to using them for breeding. However, the interpretation of the results is difficult, since many adult Boxers have some abnormalities detected on at least one of the tests and there is no available information regarding the relationship between these findings and the likelihood of development of clinical signs. The objective of this study is to evaluate the correlation between specific cardiac parameters (Ventricular Premature Contractions (VPC) number, grade of arrhythmia, heart rate, etc.) detected by electrocardiogram, ultrasound, and Holter monitoring and the development of clinical signs including fainting, sudden death and congestive heart failure in 130 adult Boxers previously diagnosed with heart disease.