Is heavy cardio the only way to burn fat from metabolic syndrome?

No. Circuit weight training is quite effective, as is traditional resistance exercise with either machine or free weights. I personally lift weights and mountain bike! The combination is better, less boring, than doing only one. But you must free yourself from sugar and starch!
No nutritional Rx. Eat only meat or fish or cheese or eggs or poultry and low starch veggies, drink only water. In other words avoid all carbs, carbs will raise your sugar levels and then your Insulin levels. The fats in the meat or fish or cheese or eggs or poultry will act like a "log on your metabolic fire" to keep your blood sugar stable for hours without raising insulin.
Exercises and Diet. Only way to treat and improve metabolic syndrome including all the conditions is combination of exercise programme and proper nutrition, life long to loose weight and abdominal girth, Insulin resistance, high BP and lipid abnoemalities.

Related Questions

Is cardio the only way to burn stomach fat from metabolic syndrome?

One way. Low carb diets are the best. Cardio and resistance exrcise are very important, and a compbination works best. Remember, if not on a low carb diet, you must run a calorie deficit. And consider that the mouth, can outrun the best cyclist or distance runner.