What Causes Palpitation And Shortness Of Breath Upon Walking?

I m a 75 year old woman and not in very good shape. Am 5 3 and weigh 184. Husband has been encouraging me to walk more. I go about 100 yards at moderate to slow pace and get winded and heart rate goes to about 90. I m trying to walk about 10 minutes 3 times a day. Why am I so out of breath and have this heart rate level after just 100 yards? Heart reports are fine. No other health issues except was just diagnosed as slightly anemic. Would this be normal with just starting to get back into shape?