Hi Mufty, sorry Bertie is ill. Right sided heart failure has many causes and is a bit less common than left sided. Ascites (fluid retention in the abdomen) is common in people, and they often get swollen legs. Again in people, diuretics would usually be prescribed. I'm not a vet, and in any case diagnosis/treatment over the 'net isn't a good idea, but I would ask your vet why he says Bertie doesn't need a diuretic. Digoxin is also often prescribed to people, and its another thing you might ask about.
Does Bertie have an arrythmia (an irregular heart beat)? My experience with heart problems in dogs has been with left sided congestive failure due to cardiomyopathy, but when the heart failure comes on quickly in those dogs, it is very often due to a sudden arrythmia, and treating the arrythmia often leads to improvement. You say Bertie had lots of X-rays, but did he have an echocardiogram and ECG? A chest X-ray will show up enlargement of the heart, but echocardiograms and an ECG are helpful in working out what is going on and how best to treat it. Did the vet say if the problem was ventricular, atrial or both? Did he mention valve disease? Or cor pulmonale or see any problem with Bertie's lungs? Did your vet check for lungworm and heartworm? Neither are common in the UK, but they are seen in a few areas, and can cause right-sided heart failure.
If Bertie has any form of heart failure, getting rid of the extra weight is essential, but I'm puzzled by the vivitonin. It isn't a cheap drug, and as far as I know it is only marketed for use in senile dogs. If Bertie was mine, I think I'd want a referral to the nearest vet school/veterinary cardiologist asap, but failing that I'd ask the vet to give me all the information he has, including the investigations, the results and the medical terminology (ask him to write it down if necessary). If you don't know what it all means, post it here and between us we should be able to work it out

. Best of luck.