Brad Lesley -- who fashioned a sports-movie career out of a few seasons in Major League bullpens -- died of a heart attack ... NOT kidney failure, as previously believed ... according to the death certificate obtained by TMZ.
Leslie was 54 when he died in a Marina Del Rey hospital April 29, as TMZ first reported. His ex-wife said he'd been in a nursing home for months due to kidney problems that required dialysis ... and that he died of kidney failure.
But the death certificate says it was cardiac arrest that got him ... brought on by a case of coronary artery disease ... and he never had surgery for it.
Lesley spent 1982 to 1985 as a relief pitcher for the Cincinnati Reds and Milwaukee Brewers ... in the '90s, the native Californian appeared in "Mr. Baseball" and "Little Big League."