Hawthorn Berry for Heart Valve Disease in Chihuahua

I have an 11 year old Chihuahua which was diagnosed with severe heart valve disease 3 years ago. Cardiologists at Cornell gave him a few months to live and said he would NEVER see 2 years. Well, I started giving him a supplement with flax seed meal, salmon oil and some other things, as well as feeding him a good senior food and he is doing quite well. Vets also prescribed furosemide, spironolactone, and enalapril which he takes twice a day. We are even up to taking a short walks (no hills) without him passing out (which he used to do). At his last annual checkup, the vet said he was better this year than last.
My first question: I have read that Hawthorn Berry Tincture given to people with heart problems can do wonderful things for strengthening the heart and even the valves. I immediately started brewing some and am wondering if it would be advantageous to give them to my dear Mike 3 times a day, 3 drops a day? I don't want to do anything to jeopardize him and would we open to any other natural remedies that could help.
My second question: I hate giving him these prescription drugs due to fears about side effects. Is there any chance of getting him off the diuretics so that his kidneys are not threatened?

Congratulations on all your hard work so far! You might next want to look at the use of a good, homemade diet to increase the bioavailability of nutrients in your dog's meals which in turn may strengthen his body as a whole. Please see the work of Richard Pitcairn, "Natural Health for Dogs and Cats", "The Complete Herbal Handbook for the Dog and Cat" by Juliette de Bairacli Levy and "The Barf Diet" by Ian Billinghurst for further information and recipes.
As for the hawthorn (Crataegus oxycanthus), yes, it has been used in both human and veterinary medicine to increase the efficiency of the heart muscle, most notably in congestive heart failure and hypertension. There is some thought that the possibility of an interaction between anticoagulant medications and antihypertensive drugs could theoretically exist, and of the latter, enalapril is one. However, this is speculation only and has not been proved. The standard dosing for hawthorn tincture (strength = 1:2 or 1:3 in a 25% alcohol base) is typically 0.5 to 1.5 ml per day per 10kg (20lb) of animal, optimally divided into three portions. It would be prudent of you to start at the very low dose you suggest of one drop, three times a day and slowly build up to the amounts mentioned above, depending on your dog's weight and monitoring him the entire time for any signs of heart problems (trouble breathing, loss of energy, fainting, etc). It might also be a good idea to let your vet know you are administering this herb as well.
Regarding your question about weaning him off the drugs, I cannot comment. These are powerful medications and would need to be monitored by a qualified professional in your area. Should you be interested in such a person, you could look under "Find a Practitioner" on the website of the Veterinary Botanical Medicine Association (www.vbma.org)