I’m an RN and I don’t know how much of this is true for dogs but for humans the main danger in a heart murmur is that the blood gets swooshed around in the heart and the trauma to the blood cells causes them to coagulate, leading to blood clots. With people we don’t want them to do anything that might cause the blood to coagulate more easily so we avoid foods with high vitamin K, which are your dark green leafy veggies. Dark green is OK as long it’s not leafy (so peas and green beans are still OK but avoid spinach, kale, broccoli etc.). Of course with any heart problem you need to really watch the sodium.
