Warm the cockles of the heart

This is one of the most expressive idioms in the language meaning to suffuse with a warm glow of pleasure. The expression has been around since the mid-17th century but its origin is debatable. The OED says the most likely explanation is that the cockleshell is somewhat heart shaped, supported by the fact that the zoological name for the cockle is cardium from the Greek for heart. Another theory is that it derives from a mispronunciation of cochleae cordis, which is the Latin medical term for the ventricles of the heart. Quite why a fairly well known expression should derive from a little known medical term has not been explained. Cockleshells are undoubtedly heart shaped and this remains the most likely explanation.