Heart failure was a medical condition where the heart fails to supply sufficient blood flow to meet its body's needs. It is sometimes confused with cardiac arrest, which can cause heart failure but is not the same thing. It can cause death if not treated.
Bajoran First Minister Kalem Apren died of heart failure in his sleep in 2371. (DS9: "Shakaar")
Fear could also lead to heart failure. In 2372, some of the Kohl settlement inhabitants experiencing a virtual reality program died from massive heart failure. (VOY: "The Thaw")