This heatmap visualizes cardiovascular disease case counts across ten countries from 2018 to 2023. The SVG rendering uses D3.js version 7, specifically `d3.csv` to load external data and `d3.scaleSequential` with `d3.interpolateReds` to map case numbers to color intensity. Each cell represents a country-year combination, and hovering triggers a custom tooltip with detailed values. The legend shows a low-to-high gradient, while the dataset is sourced from a remote CSV file.