var myObj, i, j, x = "";
myObj = {
  "name":"John",
  "age":30,
  "cars": [
    {"name":"Ford", "models":["Fiesta", "Focus", "Mustang"]},
    {"name":"BMW", "models":["320", "X3", "X5"]},
    {"name":"Fiat", "models":["500", "Panda"] }
  ]
}

for (i in myObj.cars) {
  x += "<h1>" + myObj.cars[i].name + "</h1>";
  for (j in myObj.cars[i].models) {
    x += myObj.cars[i].models[j];
  }
}