True about metastatic calcification -
Calcification

The deposition of mineral salts of calcium is a normal process in the formation of bone and cartilage. Calcium entry into dead or dying cells is usual, owing to the inability of such cells to maintain a steep calcium gradient.

Pathological calcification

Pathological calcification is the abnormal deposition of calcium salts in soft tissue.
It is of two types

A) Metastatic

Metastatic calcification reflects deranged calcium metabolism.
It’s a change associated with an increased calcium concentration in the serum.
In general, almost any disorder that increases the serum calcium level can lead to calcification in locations as the alveolar septa of the lung, renal tubules and blood vessels.
The fundamental abnormality is the pathological entry of the same amount of ionic calcium into the cell organelle, chiefly the mitochondria (it is suggested that mitochondria are the organelles first involved in the pathogenesis of metastatic calcification).

Sites of metastatic calcification

Basement membrane & tubular lamina of kidney
Alveolar wall of lungs (most common site)
The interstitial tissue of gastric mucosa
Systemic arteries
Pulmonary veins
Cornea & conjunctiva
Synovium of the joint
Tendons
These sites are prone to calcification because these tissues loose acid and therefore have the alkaline internal environment. Alkaline pH favours precipitation of calcium salts.

B) Dystrophic calcification

Dystrophic calcification refers to the macroscopic deposition of calcium salts in injured tissues. This type of calcification does not simply reflect an accumulation of calcium derived from the bodies of dead cells but rather represents an extracellular deposition of calcium from the circulation or interstitial fluid. 
Denatured proteins in dead or irreversibly damaged tissue preferentially bind phosphate ions. Phosphate t ions react with calcium ions to form a precipitate or calcium phosphate. Thus necrotic tissue serves as calcium sink.
In many locations such as in a case of tuberculous caseous necrosis in the lung or lymph nodes, calcification has no functional consequences.
Dystrophic calcification may also occur in crucial locations such as in mitral or aortic valves after rheumatic fever. In such instances, calcification leads to impeded blood flow because it produces inflexible valve leaflets and narrowed valve orifice (mitral and aortic stenosis).
Dystrophic calcification in atherosclerotic coronary artery contributes to narrowing of vessels.
Dystrophic calcification also plays a role in diagnostic radiography,
Mammography is based principally on the detection of calcification in breast cancers.
Diagnosis of congenital toxoplasmosis and infection involving the central nervous system is suggested by visualization of calcification in the infant's brain.
Serum ca level is normal
Occurs in dead/dying tissue
Occurs in damaged heart valves
Calcification starts in mitochondria