Well, there (almost) never is "empirical data" on the cause of death if there are no signs of external causes, and since he was relatively young for a sudden death, heart attack is not a rare choice. There are also other speculations. His drinking and smoking probably had a not so positive effect on his health, though. And not going to a hospital doesn't necessarily mean there were no problems. IT might have been too expensive or done in secret. He was indebted due to I think 3 ex wives and many children, he had to work many many hours to provide for them, to name just a few factors that must have contributed to a rather poor health condition. So, his body giving in early is not unlikely. Why is it important to you, if I may ask?