I Have Pacemaker Installed And Has Been There Now For

I have pacemaker installed and has been there now for 6 years. I am getting short of breath and a feeling of nausea. I recently had a scan and it appears that my heart is not expanding and contracting as it should. I am 70 years of age, normally very fit, walk 6 kilometres a day, travel twice a year to Tibet to climb and do high altitude trekking.