Is garlic really good for the heart, and if so, why?

It depends on what sort of heart problem you think you may develop. If, say, you fear a clot in your coronary arteries (a coronary thrombosis), then enzymes in garlic (thiosulphinate and allicin) help prevent clots forming. Cooking garlic for more than five minutes destroys them, however, and you have to crush the garlic first (to break down cell walls) to make the enzymes available for digestion. So eat nearly raw crushed garlic to get the best out of it. On the downside, if you bleed too easily, or if you are taking a prescribed anticoagulant, crushed raw garlic may make things worse. It's a matter of balance between clotting and bleeding. As for the claim that garlic lowers cholesterol levels, recent studies refute it.

What's this about extra vitamins shortening lives?

Studies to see if vitamin supplements would reduce deaths from cancer and heart attacks were stopped after a few years because more people in the groups taking the supplements (notably beta-carotene) were dying than in the groups taking a placebo. I'm surprised companies can still market beta-carotene as a supplement to the public. If a prescription medicine had had similar trial results, it would have been taken off the market. I see the vitamin makers call the trials 'fatally flawed', though I don't see the flaw in the published papers. I'm also sceptical about the claims for antioxidants. We get plenty of vitamins from normal food without popping pills.