Idiopathic mitral valve prolapse (MVP) is the commonest valvular disorder in industrialized nations. It is predominantly a familial condition, showing Mendelian dominance with delayed and variable penetrance. Although hyperkinesis and hypertrophy of the left ventricle have been described in MVP, its histopathology, somatic morphology and genetics support the leading theory that MVP results from a hereditary disorder of connective tissue. Latent tetany (LT) due to chronic Mg deficit (Mg-D) occurs in over 85% of MVP cases; MVP complicates 26% of LT. Mg-D can explain many clinical features of the MVP syndrome which are not easily explained by its genetics. Mg-D hinders the mechanism by which fibroblasts degrade defective collagen, increases circulating catecholamines, predisposes to cardiac arrhythmias, thromboembolic phenomena and dysregulation of the immune and autonomic nervous systems. Mg therapy provides relief of MVP symptoms.