Hello and welcome to the forum. Sorry to hear about your heart attack and we hope you are recovering well. Yes, coffee is generally considered a fluid and count toward the count. Remember that you are trying not to make your heart work as hard. For dry mouth, try a piece of sugar free candy. Are you taking diuretics that are trying to reduce your overall fluid volume? Are they telling you that you have heart failure by the way? https://www.heart.org/en/healthy-living/healthy-eating/eat-smart/nutrition-basics/aha-diet-and-lifestyle-recommendations and a basic recovery guide for heart attack. https://www.heart.org/en/health-topics/heart-attack/life-after-a-heart-attack/heart-attack-recovery-faqs
However, I'm wondering if you have congestive heart failure and this is why they are restricting your fluid?