There are multiple types of valvular disease in dogs such as mitral or tricuspid valve disease, aortic stenosis and pulmonic stenosis.
The most common is mitral valve disease; this disease is degenerative and causes thickening/retraction of the mitral valve, which is between the left atrium and left ventricle.This results in abnormal or turbulent blood flow which results in an abnormal heart sound detected on physical exam called a murmur and can lead to potentially life-threatening sequelae such as left-sided congenstive heart failure, ruptured chordae tendinae, or pulmonary hypertension.
In cases of suspected mitral valve disease, radiographs can reveal enlargement of the left atrium. Ultimately, cardiac ultrasound (echocardiogram) should be performed to evaluate the pet.
1)Veterinary Partner. Veterinarypartner.com
2)Tilley, L. P., & Smith, F. W. (2005). The 5-minute veterinary consult: Canine and feline. Philadelphia: Lippincott Williams & Wilkins.
3)Yin, S. A. (2010). The small animal veterinary nerdbook. Davis, CA: CattleDog Pub.