Mangal Dosha is the most misunderstood concept in astrology. Location of Mars in 1st, 2nd, 12th, 4th, 7th and the 8th house in the horoscope causes Mangal Dosha. It is believed to cause misfortune to the native post marriage. This dosha should be assessed from ascendant, Moon and Venus. It is known to be strongest from the Venus, little less strong from Moon and least strong from ascendant.

• Mars if present in the second house of family & speech influences the eight house of longevity of marriage.
  
• Mars in the fourth house may cause unhappiness in family life.
  
• Seventh house is the house of marriage. Presence of Mars in seventh house may mean aggression in marriage
• In the twelfth house, Mars can have a bearing on sexual pleasures of married life.

If Mangal dosha is found in both the matching charts, it gets cancelled. And if one chart has Mars in 1/2/4/7/8/12 house and the other has Saturn, Rahu or Ketu in any of these houses, still it gets cancelled.   

Astrological remedies have been prescribed in Vedas for afflictions and deficiencies of the horoscope. Manglik Dosha or Mangal Dosha too responds very well to the Vedic remedial measures.