The term 'weak heart' can be described by THREE 5-letter words: 'FRAIL', 'BRITTLE', and 'TIRED'. FRAIL means easily broken or damaged, BRITTLE implies being fragile and easily broken, and TIRED implies being exhausted and lacking energy. All THREE words describe a weak heart, which is a condition in which the heart is unable to pump enough blood to meet the body's needs. This can lead to fatigue, shortness of breath, and other symptoms.