Eating one banana and an avocado a day may prevent hardening of the arteries that can result in heart disease and death researchers have found. The study conducted on mice showed these foods that are rich in potassium reduces vascular calcification -- common complication in both heart and kidney disease. Calcification happens when calcium builds up in body tissue blood vessels or organs. This buildup can harden and disrupt your body's normal processes. A potassium rich diet also reduces the risk of aortic stiffness -- a classic cardiovascular risk factor. The hardening or stiffening of the arteries is called arteriosclerosis.