What should I do after the death of my friend, who suffered from a heart condition, following an angry verbal altercation between us?

You are not liable for a guarantee, blood money, or expiation for killing. However, the sin varies depending on the nature of the dispute. If you knew about your friend's illness and predominantly believed that he would be affected by the dispute, and you intentionally caused him harm, then you are sinful. But if you were unaware of his condition or the consequence of your argument, and you did not intend to harm him, then there is no sin upon you. In any case, seek forgiveness for yourself and for your friend, and frequently supplicate for yourself and for him for pardon and well-being.