I lost my grandfather on my mom's side just before I turned 13. He was in the hospital for a few days for something that wasn't really life-threatening, but he ended up dying of congestive heart failure.
I lost my grandfather on my dad's side the summer after my freshman year of college. I saw him during Christmas break and everything was fine. He was supposed to go for a prostate exam in January and didn't. Then in February, my grandma called my dad because my grandpa couldn't move. He called an ambulance and he was admitted to the hospital and later a nursing home. He was diagnosed with prostate cancer that month and given until August to live because it was in a later stage. He died that June.
Fight for the cure of heart disease and cancer, and guys, get checked regularly!