My father in law had a heart attack and a pneumothorax. how can those be related?

Not: They're probably not. Pneumothorax may develop as a complication of treatments for heart attack. He may be so unlucky as to have both spontaneously occur simultaneously but that's unlikely.

One Triggers: If a person has emphysema and develops a spontaneus pneumothorax that progresses to a tension pneumothorax, the cardiopulmonary stress can trigger a myocardial infarction if coronary artery disease is present. Otherwise, two separate independent events.