what is " Tugs at the heartstrings " ?
"The hospital's plea for donors tugged at the heartstrings of millions
of viewers."

Question

what is " Tugs at the heartstrings "  ?
"The hospital's plea for donors tugged at the heartstrings of millions
  of viewers."

Answer

Think of a string attached to your heart. If it is tugged slightly, you feel something.

Answer

to cause strong feelings of affection or sympathy He looked into his son's smiling eyes and felt a tug on his heartstrings. 
f something tugs at the heartstrings, it makes you feel sad or sympathetic towards it.

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give you my heart on a string means that you will give them full possesion of your heart you are pretty much telling them that they own your heart and they have the ability to do what they please with it the string meaning control and interpreted as so.(http://answers.yahoo.com/question/index?qid=20081125153932AAPTDN2). 
This term means to really get to you emotionally
deepest feelings or affections
Origin: orig. tendons or nerves formerly believed to brace the heart

http://www.yourdictionary.com/heartstrings

Answer

If something tugs at the heartstrings, it makes you feel sad or sympathetic towards it.

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هده عبارة تعني أن شيئا يحرك المشاعر