Hi welcome to Healthcaremagic,
From the scenario I get from your question, I feel that the heart burn your uncle had 2 days back must have been an initial
heart attack which went undiagnosed. As you said he took
ranitidine for the same. Ranitidine as you think doesn't aggravates a cardiac event. I doesn't have such fatal side effects on heart.
But the heart attack that went untreated must have weakened his heart that the second episode 2 days later got fatal. This must have been avoided if the initial chest pain was evaluated with an ECG and Cardiac enzymes rather than going for a Ranitidine. I think this was what your doctor also ment.
Now if you want to know on the side effects of Ranitidine I shall list a few -
allergic reaction,easy bruising or bleeding, vision problems,
sore throat, low fever, loss of appetite, swollen or tender breasts and diarrhea or
constipation. But these side effects are very rare.
Please do reply in case you have any doubt.
Thank you.