What causes heart murmurs?

Heart murmurs are sounds that result from turbulent blood flow in the heart. The following are conditions that result in heart murmurs:

• Congenital physical defects of the heart.
• Physiological murmurs that are not associated with any disease or defects.
• Hypertrophic cardiomyopathy (disease resulting in an enlarged heart), common in Maine Coons. 
• Anaemia – the blood is thinner resulting in a more turbulent blood flow.
• High blood pressure.
• Hyperthyroidism (overactive thyroid), common in older cats.

Only a heart ultrasound (known as echocardiography) can detect what is causing the heart murmur.