Casillas suffered the heart attack in May 2019 while at Porto and has not played since. Less than three weeks later, his wife Sara Carbonero announced that she had ovarian cancer and was to undergo treatment.
Mourinho and Casillas famously clashed at Madrid to the point where the legendary keeper was dropped in favour of Diego Lopez but have repaired their relationship in recent years -- but the ex-goalkeeper said his former manager was one of the first to contact him on both occasions.
"You can become closer to people perhaps you weren't as close to before," Casillas told ESPN Deportes of the aftermath of his heart attack.
"A lot of people don't know for example that my old manager Mourinho was the first person who was concerned with what happened to me and then later with my wife."
Casillas, 39, has gone on to make a full recovery from his heart attack while Carbonero finished treatment for her cancer in November 2019.
He announced his retirement from football in August after a career that saw him win three Champions League titles, five La Liga titles, two Copa del Reys, four Spanish Super Cups as well as the UEFA Super Cup, FIFA Club World Cup and Intercontinental Cup on two occasions each
"I've seen people again that I hadn't seen for a long time. You value the day-to-day more," he added, when asked how life had changed.. "You're not stuck thinking about what to do tomorrow or next week. It's just about what today will bring and enjoy the moments more. I was very lucky for whatever reason. Others have not been
"I felt that I was definitely going to die that day, and the circumstances forced me to reconsider everything. I'm a privileged person."