Mackenzie

“For Mackenzie, what mattered about the heart clinically was what he called the reserve force of its muscle, physiologically speaking its capacity to maintain the correct degree of tonicity, contractility, etc., to produce a normal circulation. . . From this point of view, valvular disease or hypertension were only important ‘as a source of embarrassment to the heart muscle.’ Heart failure, therefore, was the inability of the heart to deliver blood to the tissues. This account, the forward pressure theory of heart failure, considered diminished cardiac output as the defining feature of failure, not back pressure owing to the accumulation of blood behind a damaged valve” (Lawrence, 15).