This is called intractable or severe angina, the severity of which is designated by classes.

Researchers believe the loss of these blood vessels contributes to the pain of chronic, severe angina.

The therapy, carried out by Chicago's Northwestern University, halved the number of bouts of angina chest pain.

Patients with severe angina had stem cells from their blood injected into their heart.

Viagra can be fatal if used in combination with nitrates, the drugs prescribed to treat heart problems such as angina.