Arm Cramping In Hot Weather With Breathlessness, Painful Chest, Blackouts And Over Weight. Suggest Reason?

Hello. when it gets warm outside (sometimes 80°F, sometimes 90°F) my buddy experiences cramping of the hands (reason for me typing in the question), strong tingling feeling in the arms and complete numbing of the hands and he suffers severe shortness of breath. His chest also hurts and he has momentual visual blackouts, his field of view literally blacks out a few times, and for a few seconds each time.. He is 50 to 60 lbs overweight , has had three small heart attacks (he is twenty six, the bad heart from early child age on runs in the family) and was in the sun when it happened, at the playground with his little daughter to be precise.