Side effect of contrast medicine.

I am suffering with atrial fibrillation and grave hyperthyroid for over 18 months. I feel pain on chest when I bend or heart is pressed. But i do not feel pain on chest when walking straight and i can walk for kilometers without pain on chest.  I was told earlier by aathma doctor that my heart is enlarged and it press against lungs. Now my questions: Question 1. Do I need to do  CT Coronory Angiography test to check blockage in arteries? Can pain in chest while bending caused due to blockage. Question 2. Can pain be caused in chest due to enlarge heart which is pressed while bending. Qhestion 3. Lab people told me that Contrast medicine will be given before test and to accompany someone before test. I have multiple health problem like asthma, atrial fibrillation and grave hyperthyroid. Is there any side affect of contract medicine. Please answer all 3 questions.