I want to convert the output voltage of an ECG (-5 to +5) to 0 - +5 volt for ADC. Should i use Op amp ? What is my problem in this picture? I simulated it in Proteus ... but when input voltage is higher than 4 V or lower than -4 V Vout gives an unexpected value. 
Below is another simulink that have same problem ... 
My idea to make this level of voltage is (Vin +10)/2 that give the range 0-5 V.
Answer
The 741 can't accept an input that's too close to the negative rail. The data sheet says the input range is +/- 13V when the power supply is +/- 15V. Not sure about when the negative power supply is 0V but I doubt it will work the way you expect with a 0V input. Similar story on the output side. That would explain the strange numbers you're getting below -4V input. Don't know what's going on with the +4V input since there would seem to be plenty of headroom with your +12V supply. Does the simulation work if you power the 741 with +/- 15V? It looks basically correct if you assume that the op amp is ideal.
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