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A substantial proportion of measured resting left ventricular diastolic pressure stems from forces extrinsic to the left ventricle rather than from diastolic stiffness in the left ventricle itself. This markedly influences the dependence of cardiac output on filling pressure and has important implications for clinical application of the Starling law.

To evaluate whether the incidence of acute myocardial infarction (AMI) attack would have circadian, weekly and monthly variations in a subtropical area, 540 consecutive patients with AMI who were admitted to our coronary care units were analyzed. Six-hour intervals over 24 h, daily intervals in a week (7 days) and monthly intervals in a year (12 months) were studied, respectively. Results showed that there was a circadian variation in the onset of AMI with a morning (6 a.m. to noon) peak (34%, p < 0.01) but no secondary late evening (18–24 p.m.) peak. The incidence of AMI was significantly lower on Sundays (9%) than on the other weekdays (Monday through Saturday; p < 0.05). However, no monthly and seasonal variations in the incidence of AMI (no winter or summer peaks) were observed in this series. This study demonstrated a circadian variation in the onset of AMI attack with a predominant morning peak. The fewer AMI cases on Sundays compared to the other weekdays suggested that freedom from ‘stress’ or ‘work-load’ on Sundays might have an important impact on this low incidence of AMI. Unlike the large ranges in cold or hot weather found in temperate regions, the warm climate of a subtropical region does not affect the frequency of AMI.