Restrictive Cardiomyopathy is the rarest of the cardiomyopathies. This condition gets its name from the way it restricts the heart from stretching properly. While the rhythm and pumping action of the heart may be healthy, the stiff walls of the heart chambers keep them from filling normally. So blood flow is reduced, and blood that would normally enter the heart is backed up in the circulatory system. In time, the heart fails.